Does Haskel ability to solve "hard" problems makes it somehow unfit for solving "easy" problems?
Or, to put it the other way, why do you think it can solve "hard" problems if it can't even solve "easy" problems?
Not to get into the whole Blub language argument, but I daresay the average Haskell programmer is more advanced then your average web programmer. This is not to imply the latter is somehow easier or trivial (working IE support? I'm not ever gonna call that easy....) but it could explain a different focus of the community. Resulting in less webprogramming being done. That said, I've seen 5i7 Haskell webprogramming frameworks pop up in the past 2 years, so I'm not the only one who thinks it is perfectly suited for that.
http://www.yesodweb.com/ http://snapframework.com/ http://happstack.com/index.html http://blog.on-a-horse.org/
I am sure there are more.