"As we work toward the release of the PC version, Games for Windows Live affords us the opportunity to seamlessly translate the multiplayer console experience for PC gamers," said Rockstar founder Sam Houser. "The service is a natural fit for the platform and we strongly believe it will help in building a strong online community around GTA IV PC." According to the Microsoft, GTA 4 PC will benefit from upcoming Live features such as "a redesigned game interface, out-of-game client and marketplace."
The port is set to feature graphics improvements, a new replay/clip editing mode, and multiplayer additions.
If I was a GTA fan, I'd be pissed right now.