I highly doubt rockstar would have neglected a PC release anyway, since the entirety of the GTA series that has been multi-platform (ie on both xbox/360 and ps2/3) have also made it to PC. They ported IV (to whatever standard) despite using an entirely new engine, and despite that fact that coding on that new engine for new systems was probably pretty draining. Yeah, we didn't get red dead, and we don't know why... but it was a new franchise and maybe the guys upstairs (T2) wanted it that way. Max Payne 3 made it to PC, and the port was apparently pretty good, with a handful of sources making comments about the loading times, (I happen to think if you complain about load times in a game you're an idiot but hey.) which indicates rockstar have had a little more experience with the engine and are prepared for a PC release.
On top of this, not releasing to PC when the modding community is so prevalent is commercial suicide. GTA has one of the most dedicated fan bases there is, people still regularly play, create content for and make machinimas and so on for SA as well as IV. They're an intelligent company, very aware of the industry in which they operate and I think they know what the right decision is from both an image and financial standpoint.