This is wrong on so many levels.

No reason you can't, but you'd have to be using a desktop that supports it. For a while I ran a 3 wide, 2 high desktop using fvwm on my N800 back in the day -- you could certainly do the same on an N900. You could probably, with enough work, also hack the hildon-desktop to support it (which is presumably what you're after), but you're talking a lot of work for IMO not much gain.

In practice, the main reason people use large virtual desktops is not so they can pan half-way between them and look at widgets in odd locations on the screen. It's usually so they can use an app with a larger than screen window (and in fact this was part of the reason I ran fvwm that way). Since windows in hildon are always full-screen, this doesn't apply, and I think most people would rather a given widget is either off-screen, or right where they put it, not moved because they only scrolled a half-screen.