I think the idea is to be a quick pick up and play game. Age of empires has always been quite an involved game that I often found if you didn't finish your opponent off quickly, the map could take many hours. Not ideal for an online game really.  I would also imagine they will expand it over time, see it as an opportunity to charge more money.
For me Age of empires 2 with all the add-on packs was the best you could get. I felt 3 really never came close to being as good.