If they're appealing to Apple, I'd say it's because they already have such a big partnership with Apple in iOS integration. For whatever reasons the partnership was appealing, an acquisition would likewise be appealing.
Maybe, but Apple would be inclined to make it Mac / iOS only, which would be counter productive. The other non Apple stuff has had a strategic importance, iTunes for windows enabled them to sell iPods and Safari for windows helped with website compatibility. Can't see this happening.
Do you think perhaps restricting 3rd party clients is a way to make them more appealing to a potential buyer like Apple?