Paying developers to port their apps is completely legitamete. It's a chicken and egg problem. Users don't want to use the platform because there are few apps, but developers don't want to write apps because there are few users. If Microsoft can spend some money to get additional apps in the store it's just a business decision. In my opinion they should have dedicated more money to that program.
This on the other hand is deceptive and I think pretty embarrassing. Completely different scenarios.
It's not quite as slimy as, say, Samsung paying for fake grassroots badmouthing of competing products [1], but it's little different from fake user reviews on Amazon, unless the blogger discloses upfront, in a very visible way, that it's a paid-for post.
Nothing wrong with rewarding developers for porting app to your platform, there is nothing deceptive or otherwise unethical about it.
The $100-per-app bounty was clearly an embarrassment.
What kind of apps did they think to get with this? Some more fart apps? Cause that is about as complex an app as you can get by spending 100 bucks on a developer.
100 bucks gets you between 1 or 2 hours of a freelancers time. There is not really that much that could be done in that time frame.
Either MS was completely naive when setting that bounty or they of course realized that this would just help inflating the total app numbers in the store. Better not mention how many of those are pure crap when boasting about how much the app store has grown in the next press release etc.
This on the other hand is deceptive and I think pretty embarrassing. Completely different scenarios.