Women are from Venus...
I should know better, but when I ask girls to go out (on a plutonic basis), they agree, and then some time between saying yes and actually meeting, they'll bring someone else with them. "I'm bringing --- along, is that okay?" At that point, the polite thing would be to say yes (because how can you say no, especially when they inform you of that ten minutes prior to actually meeting?) Some even bring up that fact only when you're already face to face with them.
That's not to say guys are less attached to company. But we usually go about it differently. Before we say "yes" to the meeting, we're already fishing for information. "Who else is coming? Who's going to be there? Can I bring --- along?" And then guys will negotiate and argue on whether they're actually going or who they're going with, but once you get them to agree, there's rarely any surprise left after that, short of an actual unforeseen event or emergency.
Moral of the lessons? Girls say yes first, then asks questions later. Guys ask questions first before finally saying yes.