That's not a fair comparison. If you want Android, you have a multitude of devices to choose from and it comes down to niche differences which one you will choose. Apple doesn't give you choice. So, obviously, there'd be less Galaxy Nexuses sold than an iPhone 4S (even though they haven't gone on sale yet, i know they won't outsell the 4S) because the consumer has more choice. Sorta like what would happen if the one of the two main political parties split. Even if there were more combined votes for Party 1a and Party 1b together, there'd most likely still be more votes for Party 2 compared with either 1a OR 1b. It's simply because you're given more choice.
Personally, I think since Samsung and Apple have different business models, it's pointless to compare any sales numbers.
Hell, I could say that on a phone by phone basis, there's no comparison because Apple doesn't have a phone that competes with the Galaxy Nexus. I mean, have you seen the size of that screen? Apple offers no products in that market. You can twist anything to make one superior to the other, but its pointless because whatever you're basing it on isn't important to someone else.