Well, you asked a direct question, so here's my 2 cents worth. I can think of two reasons. Most importantly, not everyone has a 1280x1024 display. My desktop monitors do, but my laptops don't. You have to allow for lesser resolutions, like 1024x768, say. Secondly, what's the problem with a 1cm (on a 19" TFT) bar on each side, that's not 'thick', IMHO, and it would of course be even less on a smaller 1280x1024 screen. It certainly doesn't worry me, and I often have the Favourites sidebar on anyway.
Andy
It's not what you play, it's not how you play. It's the fact that you're playing that counts.