there is absolutely not incentive on using Ubuntu phone platform. Android has already proven itself for both lower and higher end devices. Plus it comes with tons of content. Content is everything. Remember the first iPhone, it sucked before the app store arrived.+Jay Morgan
there is absolutely no reasons to run native apps if their interface is not optimize for mobile. Android is already running Linux so there is nothing new here. FYI, your already running a full computer in your pocket, it's just a different interface ;-)
What Ubuntu should have done is release a skin on top of android that loads Ubuntu when you plug it to a docking station. That way, it would already been released and they would taken advantage of the Android ecosystem. But even that would have been a risky move since Motorola tried it already with their Astrix and it was a total flop.