I wasn't lying, actually.
I think the difference with your example is that your female friends could actually sleep with you. Sex is a possibility there. With my straight friends, it's not. So while I recognize their attractiveness and we may occasionally joke about it, I don't really think of them sexually because I know that is an option which is closed to me. Perhaps it's a trained skill to prevent me from pursuing an impossibility, but it's there regardless.
Nah, I'm there to do a job, not to get aroused. I actually avoided joining a gym until college because I thought I'd get instantly turned-on in that situation, but it's just a completely different mindset that prevents it. The straight ones are little more than eye-candy to me there, and I'm usually too focused to notice in that situation unless we're talking a 9+/10.

Now it's different if I see a hot guy in the gym who I think is gay, mind you. I might investigate that a bit, and have been investigated in the past, but that difference ties into my previous point. Also my gym doesn't have showers, so I can't speak on locker room practices.