I contacted Rockstar to get the final word on the 2-player issue and it seems that RCAgent's happy frenzy of disproving me is right down the drain
Here's the part about 2 player from my mail exchange with Rockstar:
| apparently, the dual|
keyboard and mouse set up proved too unwieldy for players and didn't
work with the PC version of San Andreas' greatly improved free camera
mechanics, as such Rockstar North decided to focus on maximizing the
single player experience.