when games are measured in Gigs rather than Megs, it matters.
That may be so, but most users generally don't have multiple partitions.
Well, multiple partitions on the same drive, no. But multiple drives, and thus with 1 partition per drive, multiple partitions is probably much more common.
What is the most annoying with those installers that assume C: is all you'll ever need, is when I'm at the point where my main disk is full or nearly full, and I decide I need to buy a second one to get more space, a lot (well, not that much but certainly too many) of installers do NOT work correctly and allow me to make full use of that additional space I've bought.