I agree that Tapastic is a nice community, in the sense that people encourage each other, and if someone has nothing nice to say, they say nothing. It's a very "live and let live" attitude, and I like it a lot, even though it means that the responsibility of getting any criticism rests with the author. @shazzbaa mentioned that criticism takes effort and time, so it only makes sense the author has to put in some effort into getting it too.
I haven't gotten any critical feedback on my comic here at all, and every time a thread like "will offer critique" appears, I am always too late to the party. Bummer. There was this guy here on forums who offered his services as a reviewer/editor for a very modest sum (a price of maybe two or three Starbucks drinks) and I am honestly thinking of getting in touch with him. I also think, hey, if you really want to get better, that might cost you in the monetary department. Matter of fact, I supported Ben Caldwell's project on Kickstarter once (and it did cost me), and got a 3-hour Skype critique of my comic. He really picked everything apart and put it back together for me. God bless capitalism.
On the other hand, I host on a non-English site, and unsolicited critiques come in spades. They're usually not very nice, either, and sometimes they just hurt. Only one person asked me if they could offer me their critique, I said yes, and boy, did they - but it was also proved very useful to me. I've learned to deal with unsolicited critique by strangers by either ignoring it if it is nasty, or a curt "thank you for your opinion" if it's nice enough, but unasked for. Kind of presumptuous to just barge in and tell the author how they should be doing things, don't you think?
All in all, I think Tapastic's "niceness" is a good thing. Those who want to get better will definitely find the way to get critiques, and everybody gets some encouragement whether they want to get better or not. Win-win.