Well, what's the point of having levels 11-20 if you never use them? In pretty much every 3E campaign I've been in, we were lucky to advance 10 levels beyond where we started, and that's with full XP, even somewhat higher than normal as we took on tough challenges.
What with people changing schedules, wanting to start new campaigns, sticking alternate games into a weekly rotation, and so forth, a campaign may not last all that many sessions. I'd like to the option to play a full 1-20 campaign in a sustainable amount of time.
So IMO, a campaign that goes the full 1-30 should be the standard, with levelling speed that supports that. If anyone wants to level slower and/or start higher, that's fine, the XP rate is easy to adjust.