I don't think a photo has to make a statement or have some deep meaning to be art. To me that approach can get you into the realm of hoity-toity art; taking a picture of a trash heap and declaring it a commentary on modern society's mass consumerism might score points with the NYC art critics, but to me it's just pretentious BS. I don't see a problem with photographing beauty for beauty's sake, or capturing a fleeting moment of nice light, etc.
Russ mentions the difference between a fine art photograph of "trees and rocks" by Ansel versus a "trees and rock" photo by the average photographer; but I think the real difference there is largely one of skill, craft, and artistic vision rather than any differences in meaning. From what I've read, I don't get the impression that Ansel ascribed any deep meanings to his images beyond an appreciation for (and desire to preserve) the beauty of the natural world. I do tend to think that a good photograph will at least have a subject, but that's not necessarily the same thing as meaning.
As far as participation in the user critiques forum, I think the quality of comments here is better than any other forum I know of. People tend to be polite, but it's not all just "nice shot" comments; there are a lot of insights shared by various posters that I find valuable and interesting.
My approach to commenting is that I"ll tend to comment on the images I like, but more than just saying "nice" shot I try to describe why I like it. I will also offer criticism if there is something that I think could have improved the image, either technically or aesthetically. But there are some subjects that just don't interest me, and I don't think posting a comment to say that I find the image boring or pointless is very useful when it may be a perfectly fine photograph that appeals to people who _do_ find the subject interesting. So in those cases I'm likely to just say nothing.
Jeff, I suspect I should have quoted more of Brooks Jensen's article, but I was hoping people would read the whole thing. It's available on the web, but at the moment I haven't time to go looking for it. The book, itself, is home and I'm in my office. The burden of Brooks's argument about Ansel was that most people shoot to make a record of what they see. Ansel shot to express an idea but not necessarily a "deep meaning." He went on to suggest opening a photography book by one of the masters and looking at the pictures. His point was that with each picture you'd be able to recognize an idea.
I think Brooks is right, but... I have trouble with the word "idea" in that context. Let's put the idea thing a different way. Instead of asking for the "idea" behind a shot let's simply ask someone who posted a picture for criticism why
he shot the picture -- if the reason isn't immediately obvious. As both you and Jeremy (kikashi) pointed out, "I felt it was beautiful" is reason enough. In street photography the reason's often going to be a revealing interchange between people. In abstraction an interesting line would be a valid reason.
I agree that it would be insulting to call a picture boring or pointless, even, or perhaps especially, if the picture is boring or pointless. But people don't go around shooting pictures because they thought what they were shooting was boring or pointless. There's always an idea there, somewhere. It's reasonable to ask "why?".
I also agree with your assessment of User Critiques. There are few, if any other fora where you actually can discuss photographs as opposed to photographic equipment. This is the best by far.