Generally speaking, you get better traction with weight on top of the tires - in the case of FWD, it's the engine. However, the thing that FWD has really got going for it is that you can turn the tires in whatever direction you are heading, which allows for better cornering/turning in snowy conditions. I'm sure there are more reasons.
Really, with good snow tires you shouldn't have that bad a problem with RWD in snow, unless of course you spun sideways into a ditch (possible in any car) and need to get yourself out.
On a side note, it is my opinion that everyone should have at least one shot driving in snowy/inclement weather. I went out with my freshman year roommate, who's from Maryland, during his first time driving in snow (driving his 5-speed 2000 Maxima, no less, though this was three and a half years ago) and it was highly amusing watching him spin the tires at 5500 RPM in first gear trying to get up his first hill.
