Microsoft's new store didn't explode onto the scene and suffers from a lack of content, with only 800 apps released so far. That's a drop in the bucket compared to their closer competitors like the Android store, and unfathomably less than the current trendsetter in the mobile app world, Apple. Whether or not the introduction of an app store will help improve the situation for Microsoft remains to be seen.
For now, Windows Mobile has a rough outlook. Market share has dropped by nearly a third in the past year, falling from 11% to 7.9% worldwide. RIM and Apple consumed much of that loss, both companies increasing market share significantly. Even if Microsoft is late to the game, creating a store was both a critical and required step.