Just like all other stats, Expertise has both a rating and an actual value. The rating conversion is designed to scale with level so that gear becomes weaker as you gain levels, thereby forcing you to upgrade.
You can also gain Expertise from racial abilities and talents. Your final Expertise is the sum of your racial abilities, talents, and the conversion from your Expertise Rating.
I confess that the Armory tooltip you are showing above is a bit confusing; if I read it right you have 27 Expertise Rating from gear and an extra 52 Expertise from talents, which doesn't sound correct. Is that belt your only Expertise gear, or do you have other gear that gives it to you (from stats, gems, or socket bonuses)?