as most have already said: pete's just never been as dominating before as roger is these days. put sampras on clay and he'd struggle against guys like montanes or portas. put roger on clay and he would't lose a set even if they'd play for years. that being said: roger's at least as good as pete on every other surface.
and at last: just take a look at how easily he's been outdistancing the no. 2's over the last 3 years. there's never been any talk like "wow, could the gap be narrowing?"
the first guy who slightly brought that issue up was roddick during this year's ao (remember him saying "i don't know if the gap has narrowed, but it surely hasn't widened over the last months"). and what did he get? a hell of a beating in the semis.
to me there's no doubt about the fact that roger will BY FAR be the best man that's ever played this sport if he continues to play the way he's doing right now. plus: he won't be like clijsters, the williams sisters or maybe hewitt lateron, who're talking about retiring or getting caught up in other business and therefor not focussing on tennis. fedex loves tennis, there's just no way that he'll be off stage in 2 or 3 years.
keep 'em coming, roger!