This was my thought, too: there seems to be a limit beyond which memcached simply breaks. I learned this 5 years ago, and it had nothing to do with Python.

Well, if there are too many users of an existing library, it makes it hard to do large changes. So in their case, it seems like the original library would silently fail on exceptions, they want to make things bubble up to the top which could be bad for a large number of users who have been depending on the silent-fail operation.