It's difficult, but it's mostly doable, and more importantly, necessary. People don't read, and even if you had a longer description people aren't going to read more than a few lines of it. So instead of losing out because people didn't read the whole of your description, I see this as an incentive to place everything within the region people will read.

However, I do agree that with apps of increasing complexity (WaveSecure comes to mind), you'll have to leave out a lot to fit in the space. In these cases though, I feel the rating and comments should give the user enough push to try the app, after which your app can describe itself all it wants.