The fact that R* refuses to acknowledge the existence of a PC version, to me, means one of two things:
1. They DO NOT have a pc version or next gen version in development.
2. They DO have a PC version in development but may not be able to show it or speak about it due to it possibly being tied up in some form of exclusivity with a NEXT GEN console.
Think about it. The game was delayed to the fall - the game is incredibly amibitious for current gen - and they have done exclusive stuff in the past like with the GTA 4 dlc. IF they are developing a next gen version, obviously they wouldn't want to reveal the PC version NOW because it will just make the next gen versions look the same or possibly even worse.