I've never used a screen protector on my HD2 and I've had it since December '09. It has no scratches on it and I've dropped it a couple of times, thankfully without damage. The HD2 does not have the benefit of so called Gorilla Glass.
I plan on getting the sgs2 so long as no massively unfavourable reviews suddenly appear (and this seems unlikely) and I can't see myself getting a screen protector.
I feel screen protectors were useful in the old resistive screen days, but with todays capactive displays I don't feel the point is there as much....
The only caveat I can possibly think of and which doesn't apply to me, is if you keep it loose in a bag or in the same pocket as keys. Even then, and as you mentioned, I don't think it would matter. Gorilla Glass is named that for a reason.
Samsung Galaxy S2