Leveling via PvP is a hard-fought battle in WoW, XP gains are unpredictable, and unless you're using heirlooms you risk falling behind in gear gains and gold gains. So this change, put in place by Reward Systems Designer Russ Petersen, allows those players to keep up with their PvE-ing counterparts. It's fantastic news! I'd love to see some improvement to XP gains from battlegrounds, too.
And let's not forget that Holinka has previously hinted at Skirmishes being potentially available for leveling, which would be an incredible change. Certainly, the rewards would need to be ironed out, but that they're even thinking about it gives me hope for PvP leveling becoming something that more than just the dedicated or foolhardy undertake.