Fred, I think we need to get our definitions straight before we go too far into this subject. By definition a "pro" photographer is someone who makes his living by photographing. The term doesn't imply good work. It implies paying work. There are pros who make exceptional photographs. Rob's one of them. Then there are the others. You can walk down main street in nearly any American town and see the others. I don't know if the same thing's true in Spain, but I'd be willing to bet it is. I suspect one reason most portrait and wedding studios produce the same dreary cliches over and over again is that the same dreary cliches are what their clients want, because as far as their clients are concerned those dreary cliches are what they recognize as "wedding" photographs or "portraits." Cartier-Bresson made some of the best portraits I've ever seen. So did Walker Evans and Elliott Erwitt. But if their clients had been like the average U.S. client, they'd have been out of the portrait business in no time. The bottom line is that "professional" doesn't imply "good."
In the sixties I did professional work on the side for a couple years. I did weddings, portraits, the debutant's ball that finally convinced me I didn't want to continue that kind of work, etc. But I also did some stuff on speculation, hoping to make some money off it. I've posted a couple examples from a dance class I did on Saturdays over a fairly long period. I found I really disliked the standard work, but I liked the spec work. I'd do that again if the opportunity arose. At this point I'm proud to be an amateur, in the real meaning of the word.
I think you're right that free time, which I have lots of now that I'm really retired from both the Air Force and from software engineering, is important. But not always. I think of people like Elliott Erwitt who didn't have Cartier-Bresson's advantage of a family fortune. He was a professional on the jobs he did as a professional, but when the daily work was done he picked up his Leica and became an amateur in the finest sense of the word.
I guess the reason I'm posting this is that I'd love to see us stop the kind of crap I see all the time in magazines like Pop Photography: "Join our workshop -- mentored by the pros." What BS. In practically every issue of that magazine I see the "pros" take a reasonably good photograph, crop, dodge, burn, and otherwise degrade it. Sometimes they're right about the changes, but rarely. It's time to stop calling novice photographers "amateurs," and start calling them what they are: "novices." The "pros" in magazines like Pop Photography are all about equipment. As Rob pointed out, equipment completely misses the point.
Being a pro does not garantee good imagery at all. As you pointed, in its strictly definition it is about income source.
Taking the same concept, the amateur photographers produce stunning images, we can see that easily in internet. The lack of limitations (client needs etc...) is an advantage in order to express artistically, simplifying we could talk about more freedom.
But that's also where good pros differ, in the hability to be creative, having a personal style and producing stunning images being limitated by factors the amateur does not have.
Taking a paralel, when I finished to study arquitecture before joining fine arts, we (the students) where all really creatives, imaginative and enthousiastic. In the summer I joined my first paid job in an arquitect agency and to my surprise, I realised that what we learned had to be "de-learned" because the professional activity had many limitations in practise.
Reaching the creativity into those professional realities is IMO where the differences stand, not specially in the image quality.
Or, taking another example that will resonate with your life: I have been a private plane pilot in the 90's for some years (only VFR). I felt passion about flying. But can you see the difference between flying the Sabre on assignment and flying the Cesna for pleasure? Of course you can. Yes, it is flying anyway, basic rules are the very same but the context is totally different. Skills required are indeed different even if a common knowledge of flying is evident. In the french army, I was in a military base call Mont-de Marsan (air Force base number 118). It is a sort of elite unit where they test the Mirage weapons. Well, at that time I could recognized any shade of a russian plane and put the name on it, wich gave me a sort of "fame" into the reconnaissance squadron , to my surprise, none of these top pilots where able to do so...They where the pros, I was the amateur teaching them the russian plane shades??!
Now, my life gives me a very good oportunity to see those differences and that is why I understand Rob. I have been an amateur for many years, and now I'm also an assistant of a top spanish fashion photographer, and beleive me I can observe the differences from the field.
You are right Russ, image is not, and should be not, where the basic differences between a pro an amateur are. Although the kind of imagery that do some pros is simply not possible for an amateur because of the budget involved behind (few photoshop retouching by the way). The differences are in other lands than creativity itself. It is about the hability to lead a team, to understand client needs...things like that.
A point that James Russell and Rob have stressed many many times here and that I confirm, is the very little interest, if not lack of knowledge (if we can call that knowledge) in some cases, about camera gear by those pros. Yesterday I took a coffee with 2 top printers that work with 300m2 sizes prints on aluminium for cities projects. These people are on the very top knowledge about printing and one only has a Canon G9 has a main camera. Well, we where talking about resolution, camera gear, files etc...really, they told me this: you can start with any 5MP camera, as long as you know how to do...One has heard about the Olympus PR1 he told me...I said "what?, are you talking about thye EP1?".
Anybody in a forum like this one would laugh if you write "what about the new Pentax 564 ?" But some of the very best pros I met so far would probably make the mistake, so did the top army pilots about russian planes.