At my work, I noticed a very similar issue to your point (a) when our iPhone app started to show a decent number of bugs when iOS4 dropped. 3rd party libraries

At my work, I noticed a very similar issue to your point (a) when our iPhone app started to show a decent number of bugs when iOS4 dropped. 3rd party libraries may or may not be future proof and their support may or may not be available in the future.