I need to get an info about the app/song/video by item id from iTunes Store.
I\'ve found this
But it doesn\'t work with apps.
Is there any public API
As far as I know (and I've done a lot of looking), there isn't a public API.
You're right that the HTML isn't semantically structured, so parsing it won't be very robust. But I think it's your only option. Here are a few links which might help :-
A Python script which parses reviews.
An Ars Technica article: Linking to the stars: hacking iTunes to solicit reviews.
An Inside iPhone article: Scraping AppStore Reviews.