The change means that it doesn't matter what you're waiting for. As long as you have an instance up, you are charged for it, even if it's not actually doing anything at that moment.
The multithreading change, though, will mean that a single instance will wait for multiple I/O calls to return. If these aren't charged, you'll only need to pay for that single instance and nothing more.
Unfortunately there's a limited number of threads to handle requests (like 8 per instance) and you can't create new long-lived threads. While an improvement, it's not a solution to the problem.
Supposedly it will change, but that's what's available in Python 2.7 preview. The number might be different on release, but I don't think the limit itself will be removed.
