Him: Alright, the problem stems from the fact that it's both launching on the 22nd, and each team has had to write their system to write their party system to handle party hand-offs from the OS side. So if you change the way the way the system handles matchmaking or parties or voice chat in parties or voice chat in games, you run the risk of breaking every released game's individual API, because you have to account for how each individual game's XBL functionality is written. However, the way it is now is a huge cluster mess of probs.
So, in a weird way, they can't fix it on the OS side. What you could do is you could write an all encompassing XBL-API and hand it to each dev. But then you'd have to make that the standard, the OS side would have to be patched to recognize only api handshakes from the game to the OS with that particular code. Meaning some games would still end up breaking, but it'd be fewer. And it'd be more future proof.
As a dev let me be the first to say WHO THE FUCK THOUGHT THAT WOULD BE A GOOD IDEA TO CODE IT THAT WAY