Well there must be at least 3 of us, because I'm another one. I've used the US layout ever since you could save something like 28 KBytes from not loading the UK layout, and I used this with UK keyboards for years. (Very useful having a backslash key for every hand.) Then at some point I acquired an actual US keyboard, and I was an immediate convert. I just really liked the fat Return key.
When I bought my first MBP, I wasn't completely wedded to the idea of getting a Mac necessarily - but when I noticed you could order one with a US keyboard, it tipped the balance in favour.
(For any serious work, I use a USB keyboard and mouse, so in a sense it doesn't really matter. But I use the built-in keyboard often enough that I'd be annoyed being stuck with that tiny Return key...)
(This reminded me: if you go to get a battery replacement, make sure the staff member notes that it's got a US keyboard. I took mine to a UK Apple store for a battery replacement a couple of years ago, and when I went to pick it up a few days later, it had had its keyboard replaced with a UK one! The staff member was very apologetic - perhaps they correctly read my expression of speechless shock after opening it - and it got fixed, but it took a couple more days. So in the end I was without my laptop for over a week.)