You can have a refined, bug-free, well-performing PC release after the console versions are done, or you can have a crappy, poorly optimised version day-and-date with the console release, but you can't have both. Rockstar North favour the former.
How do you explain GTA4? It was delayed a year and performed like shit on PC when it was released. GTA was originally a PC game and they have been treating PC as a second class citizen lately.