That's true. If you take a look through the "Most Popular" section of DeviantArt, you'll mostly find good art.
Additionally, there is doubtless a lot of really shitty Japanese art.
My theory is that Americans are naturally more prone to showing off, whether or not they really have anything to show off. Therefore, a lot of inexperienced (I refuse to admit these people won't get better with practice) artists go on the Internet and "show off" their bad art.
Additionally, this is the "You can be anything you want!" generation, raised by their parents to think that pretty much everything they do is great. Hence, they only get positive comments, with little constructive criticism. While saying "You suck!" is equally (probably more) useless, a good balance of positive and negative comments would be the most beneficial to these budding artists.
tl;dr: Just ignore them. The bad ones will never move beyond DeviantArt.