API churn isn't limited to small companies. The FedEx shipping API is on version 9 and my last conversation with their developer support indicated they are currently ending support for version 5 and supporting versions 6 through 9. I certainly understand that business requirements, security standards, and development practices change and that it doesn't make sense for them to support what they were doing in 1995. However, I'd expect a little bit of what Google is doing [1] in trying to build sustainable APIs. On the other hand, maybe it is a good thing for security and IT practice to have a forced requirement that the software and systems from 10 years ago change.

[1] http://news.ycombinator.com/item?id=3291136