Generally speaking, he's right. But there are alot of zones that don't fit the mold. Kaesora is one such zone. It's indoor, and an expansion zone (Kunark), but it only gives an 18% bonus. Which isn't so bad, since you're just getting out of PC anyways, so you'll want to find something with some kind of bonus to keep up the pace.
Another zone that doesn't fit the mold is Lake of Ill Omen, with a NEGATIVE bonus, roughly -5% xp. You don't notice it because of all the low AC mobs dropping like flies. Your efforts counteract the lower xp gain.