Weird, because with full BM, you can get over 11% exp. And when the next tier drops, you can get even higher. Of course I'd like to see the proof of this "10% cap", as I currently have 10.77%, and I'm missing two pieces of Champion gear.
Naturally, I assume you're pulling this out of your ***, or still think the Beta caps (you know, when you get expertise gear starting at 20) apply to Live. From what I've seen, the cap is actually 20%. But, the cap really is irrelevant because you can't reach it with the current gear in the game. BM gear is only level 60, and Valor caps at level 100. So its pretty safe to say that there will be higher tiers of gear later on, particularly because this is all subsets of Tier 1.