In reply to 1poundSOCKS:
Would you expect that having a sequence that's hard to figure out onsight would increase the grade of a route?
Because if so, you can apply the exact same argument to top-rope inspection - you reduce the route to being effectively the same as one with the same technical difficulty but with an easier to figure out sequence and hence a lower adjectival grade. But again, as with bouldering mats, we grade routes for an onsight on trad gear and take it as read that if you practice it or stick a mat underneath you're reducing the challenge to some extent.
In any case, I don't think that even the most pad-happy grithead has claimed that doing an unprotected gritstone route is as big a challenge with a mat underneath as without. I think the most anyone has said is that going for stuff onsight or ground up over pads is in some sense better or more natural than rehearsing it endlessly on a top rope and then doing it on trad gear (or lack of it), or that doing harder routes over mats is more fun than doing easier routes without. As far as that goes, I'll let you know when I've done a few E8s in both styles!
Also, Dave Mac has made the quite reasonable point that if this bothers anyone that much then they should get out to Sron Ulladale (or, by extension, Cloggy or Scafell or Bosigran or wherever) and see if they could even see a mat from the crux, let alone land on it...