Sure is easy to point fingers and blame, eh? Apple is a big target, but the fact remains that carriers play a role in this, too. Several people have stated here that the problem was resolved through a carrier update, and many others are not having the problem, so how can you conclude this is due to lack of Apple testing? Clearly it passed their tests and there's some edge cases that need to be included, such as T-Mobile et al issuing the updates properly.
It worked prior to the 7.1 update.
Who is to blame?
Did the carriers change something?
Nope. Apple changed something and the carriers had to adjust.