One of the key advantages to the Windows Store which many people overlook is the ability to showcase existing desktop software. The Windows Store doesn't only deal with metro/RT/modern applications. It can show all the existing stuff, if their publishers use it.
Here's Age of Empires Online listed. It also quite clearly is listed as desktop app. Hopefully to avoid any confusion.
The experience is much the same as for a WinRT application. Except of course you get pushed over to the applications website to install it, or to buy it. A seemless experience might have been better, like Steam. One can only imagine how long-winded and un-friendly some publishers websites are. Maybe next time.