When you are killing monsters, capturing towers and whatnot, you are rewarded with XP. Not just the WvW Xp but regular XP.
Well, even though it claims to give you this XP, you don’t actually get it.
If you check in PvE before you enter a WvW map, and go kill some monsters and capture some towers. Then go back to PvE and check again…. Your XP bar has NOT moved, the numbers are the same.
I opened a bug for this, and hope it will be fixed soon.