A couple of things that crossed my mind were:

- Maybe they're touchy about diet related posts, seeing as how that is a popular topic for spammers and affiliate marketing. I wouldn't be surprised if it raised red-flags, especially in an automated system.

- It's not all that clear that you wrote the app, though I suppose in the context of your blog that would be more apparent.

- That big Nokia logo and phone picture on the side could be construed as a Nokia ad even if it links to your live tile app.

I get the sense that while they tolerate promotion of a blogger's own products to some extent, they'd rather one didn't conduct business at all on their free hosted service. Hence the suggestion that you host your own blog if it is that critical to your livelihood.