OK, I've never thought about that and it doesn't irk me, even though I'm a pedant, but I would say it's one choice - with 2 options. 2 choices to me implies two separate decisions - so, for example, in the morning I have 2 choices to make: what to eat for breakfast and what to wear - ie two separate, distinct things. But they are used almost interchangeably from what I've observed.
Then again it seems perfectly accurate to talk about somebody's choice of clothing, for example, so maybe what I just wrote is a load of cobblers Argh, you've just made me start to worry about something I didn't remotely care about before! Cheers, tethers