This sums up very nicely the conundrum that facebook finds itself in. I read somewhere, probably on HN, an analogy that Google is like a phonebook - a place one actively is trying to seek out information and lookup things that may be purchased, so ads follow logically from this scenario. Facebook is like a yearbook or chatroom, where people are engaging with their friends, not in a search for product information or trying to shop. I'm sure this can be tweaked and messed with over time, but inevitably any attempt to try to inject shopping or advertising into communication with friends is going to be met with resistance. And that resistance level is met earlier on a mobile platform.