Not sure how an app can compete while going after only a subset of the total market.
I sense you are "right on the money" - once again - but for the last sentence. One of the things about Apple is that by hook or by crook or cross-subsidizing one venture with another, they've managed to survive as a comparatively closed-loop computing environment, because so many people, regardless of the percentages, appreciate the quality of what they offer - and I say that as an MSFT Windows user (which happened for "legacy" reasons, not because I think it better than Mac). So without knowing the economics of producing and supporting a venture like Aperture, I can still imagine it being possible that they will sell enough of these licenses to keep it in the black. Not impossible?
What I find really interesting in your post is the data on how the market has evolved. As we all know, there was a time (recent) when Mac had a real commercial predominance in the digital imaging and graphic arts community. This seems to have eroded considerably - and at a couple of PhotoshopWorld conventions I attended I've heard similar statistics to what you quote above from other people in the industry who are not related to Microsoft. So it is real. I think what's happening is that Windows has improved very considerably since the bad old days of Windows 95, such that all those people who for one reason or another think they need the predominant O/S for non-graphics related business (valid supposition or not, it's there), they are doing their digital stuff with it too and finding it workable.
Getting back On T, also interesting now that CS3 Beta is released, is to see how many features of Lightroom have turned up in Camera Raw CS3 Beta. So if we're talking about applications tripping over eachother - this two-some is even more curious than any supposed redundancy between Lightroom and Bridge, which as you say, are not even similarly purposed!
My profound regret, and I am sure I have much company, is that we will not have a "Real World Camera Raw CS3" from Bruce Fraser. This program up-grade is so substantial that his intellect and skill at explaining how to make such applications most useful to our needs will be all the more sorely missed. His passing was a great, tragic loss - quite apart from anything technical he was such a fine, personable gentleman. I hope PixelGenius will survive this and continue to do the good things you have been doing.
I know this post is a bit scattered, but in some way it is all very simultaneous in reality and at least in my mind related, so I said it as such.