The iOS dev that saw major fragmentation would have an interesting story on his hands. Statistics I've seen indicate that %90 of iOS users are on 4 or greater - http://www.maclife.com/article/news/nearly_90_percent_iphone....
I'm not sure if the bump numbers are broadly relevant: who is the average user who will be running bump? It isn't a general iPhone user, but instead is a technologically savvy individual usually in a place like San Francisco. There is no relevance there to the broader market.