I've said in other places and I'll say it again. One of the problems is that Microsoft also takes a lot of money for their dev tools. The express editions are limited with the things that can help your apps shine. AFAIK profiling is only available in VS 2012 Professional and up. $500 can be hard to justify for a moonlighting app dev. Heck I've even worked at companies where $500 for a dev tool was too much.
This is actually contrary to Apple where they give you every opportunity with their tools to make shiny apps and make their platform a joy to use.
And also I'm not saying that Microsoft should give away their tools for free. I just think that the cost is too prohibitive to individual developers who would like to make their apps "great" instead of "good enough". This could mean that the store would be full of "good enough" apps. And if it is only "good enough" why charge more?