One of the hardest things to get used to in my graduate level poetry courses was dealing with criticism in workshops. I'd always gotten all A's in English, so I'd seldom received criticism even from my teachers and professors. As you pointed out, receiving criticism is a valuable skill and necessary to the improvement of any writer.

I do think, though, that many people aren't expecting to receive criticism, even if they're putting up something publicly. My rule for myself has always been that if a friend shares a poem or story for me, I just read it and say something positive unless they've told me they WANT criticism. Blogs sort of fall into that category, I believe. People aren't expecting a workshop environment.

In the same respect, I think that people post entries in LJ Idol that they intend as finished pieces. If the deadline has already passed, the writer is not allowed to change it anyway, so they might see criticism, even constructive criticism, as being superfluous.

I like the fact that Gary has added a "work room" this season, so that those people who are seeking advice and are open to criticism can receive that. I've weighed in on a few queries in that room, and the people seemed grateful.

So... that was a windy way of saying I agree with you, but that there may be other factors going on here. :)