If they're running infrastructure that hosts game servers, while keeping all that standardized and cheat-free, that might be a bargain at $15/mo or whatever it costs. But if they're just providing match-making, listing game servers, all while hosting matches on consoles, they're just taking your money.
They've always run the infrastructure to have voice chat parties, host your screenshots/video clips and run moderation for accounts and games within the infrastructure. Cheat-free is a high bar, but its going to be less likely on an Xbox Live only game than on a user hosted server inside a PC game.
That makes sense. I forgot about voice, and the global moderation/banning features are a decent feature for something that everyone else would have to solve (with varying efficacy).