From a business perspective it's probably pretty simple. I wonder how many people bought the PS3/Xbox version and then also bought the PC version when that was released.
I know I did, I actually bought the DLC for both the Xbox and the PC, and that's probably why it's delayed, in my opinion. I also think it's easier for them to either outsource the port for the PC, or do it themselves, rather than work on it alongside the PS3/Xbox versions.
>tfw no signature