Seems like no one's really struggling to scale mobile I suspect because 1) usage, although large, is less intense and 2) much less goes over the wire (usually just data, not pages).
I think 'scaling' in this sense has less to do with data efficiency but how to develop large-scale projects for mobile, as in efficient release cycles and how to catch bugs before they go out into the wild permanently.
I think mobile app development has lots of similarity with 'boxed' products. Microsoft invests a huge amount of money in its test infrastructure for its boxed products, because once it's shipped it's very difficult to fix. I think the mobile development community incorrectly tends to treat development more like the web than they do a boxed product. For reference, more than 15% of Facebook users are using a release from 2 years ago (I will try to find the source for this info).
