You know, the vast majority of apps in the Windows Store are free, right? The Bing apps in Windows are nothing more than good templates/app versions of Bing's online services. Go to Bing Weather, there will be a couple of adverts, ect.
But that's not the future. Many are paid apps already (a lot of the free ones are pretty lame) and the intent is clearly to attract developers and have lots more paid apps. Aren't the Apple and Android models what Microsoft is trying to compete with in Windows 8?
The android model isn't comparable as the most of the whole marketplace is based off the premise of free apps. The Windows Store is more comparable to the ios/mac app stores. Except, the developers get more payoff. The Windows Store has a standard of $1.49, where Microsoft gets about 49 cents, the developer about a good dollar whereas with ios, it's roughly 30 cents for apple, about 60 for the developer; also to partly filter out crapapps.
But the better platform out of all to monetize apps is Windows Phone. Some data was recently released that shows that Windows Phone users are more inclined to purchase apps than ios or android, partly due to the fact the Windows Phone Store doesn't have half a million apps, and REAL good quality apps that are worth the while are paid ones.
But for Windows, I don't know if there is a good potential payoff for Microsoft in the long run. Seeing as most of the top titles from ios and android are free and will be and should be brought over to Windows, there isn't a payoff there. I mean, how many free, open sourced programs for Windows that can replace other costly programs are there? There's GIMP and VLC player I think of off the top of my head. Honestly, the apps that deserve to have a price tag to them should be good quality ones. I'm looking at the top paid apps right now on the Windows Store, most of them are games, a few social apps, and several productivity apps. Looking at the top free apps, they're mostly all app versions of websites, some games, a few productivity apps.
If anything in the future that will have monetization I believe will be the top latest games, and again, very good quality apps.