One of the big sells withs Windows Phone 7 is the inter-language programming allowed between things like XNA, Silverlight and .NET.
A clear example of this is a demo of a game called 'DroppyPop' developed by Andy Beaulieu in Silverlight..
The beauty of such an approach is two-fold according to Andy:
Think of it this way: instead of downloading a "trial version" of a game, he can just link you to a web version to try it out on first. Then if you want it "on the go" you can buy it for $0.99 in the Marketplace.
Case in point, just aim your browser here and play 'DroppyPop' right now.
Now don't get us wrong, this isn't so much a revolutionary game or even an amazingly compelling one, but the underlying concept of easy code portability and having a web-based version of the same game is quite impressive, if we say so ourselves.