I always thought mobile would be a massive, massive earner for Google.
1. The PC market has stopped growing. I think there's something like 2-3x more smart phones (including tablets) then personal computers, if I remember Steve Jobs talking about this correctly. The smart phone market is also growing at an accelerating rate.
2. I read the CPCs and clicks on mobile devices were higher and worth more because users are less picky and more likely to stay on a page download or buy something from that page (rather then browsing and comparing deals on different windows like on a desktop).
3. The ads on Google mobile seem to take up 80% of the screen. I only see 1 organic search result above the fold, if that. Also, if you only see the sponsored ads above the fold then that means they don't stand out in comparison to the non-coloured organic ads, which means they arn't differentiated from organic results as much.