Microsoft is slowly approaching 50,000 apps in the Windows Store, while Apple has 800,000 or so apps for iOS. Does that make Apple’s App Store 16 times better than Microsoft’s? No. Not at all.
The value of the app store is based on whether or not specific apps are available, and the underlying quality of the apps you use. Most people only use a handful of apps on a regular basis, so the other 39,990, or 799,990 are irrelevant. The fact that Apple has a diverse variety of apps available dedicated to making fart noises is no consolation for the fact that there are no Microsoft Office apps for iOS.
Apple’s App Store is better than the Windows Store, but not because it has 16 times the volume of apps. It’s because it has apps I want–like Facebook, Twitter, LinkedIn, Pinterest, Instagram, etc.. I understand that because the Surface Pro is a complete Windows 8 PC I can just use those services from the browser like I would on any other Windows desktop PC. But, that doesn’t change the fact that the Surface Pro is also a tablet, and that when I leave my office and want to use it as a tablet, I want touch-enabled apps that are designed to be used on a tablet.
Microsoft has done a great job with the design and organization of the Windows Store. There are a number of very good apps available, and the layout of the Windows Store provides a reasonable chance of stumbling across them. There are still a variety of apps, though, that are noticeably lacking for Windows 8.
Read Surface Pro, Day 6: Good, bad, and ugly of Windows Store for more about my experience with Windows 8 apps.