[mkenyon]

Microsoft does this. I have helped port a few apps that are popular on other platforms. The incentive for the company was, in fact, quite sizable.

[hrvbr]

To have the honor to be a developer on their platforms, we have to pay Microsoft 49€ per year for Windows and 99€ per year for Windows Phone. That's the opposite of a bounty.

[trimbo]

Yes, they do. I've worked at two companies where they've offered to pay for development and/or help with the ports themselves. (EDIT: for Windows Phone, though)

[msh]

We they even gave me a free phone to port over a small hobby ios app. The phone is fine but it smells like desperation.