I think this is a good topic for both genders.
DW has the ability to become easily turned on. When l initiate she always responds - well, 9 times out of 10; there have been rare occasions when she tells me it's not a good idea, although I can't remember the last time. (I know, lucky guy).
But for me - well, if she initiates sex I have always found it more tricky to respond. I can't get into it unless I am already in the mood, and over the years it has meant she initiates less. It caused her to lose some confidence in the bedroom as well.
The good news is that in the last year I've been a lot better at responding on demand. I'm not sure why exactly, and obviously it's a good thing for us both, but I regret not being able to in the past.
So I was wondering, if your partner initiates, are you able to get into it on demand? I appreciate it's more complex than the poll suggests :)