This old thing again. This has been said a hundred of times, and it has been said multiple times even in this thread. If a man is willing to engage in homosexual activities, he is gay or bisexual or whatever to at least some degree. That is a fact. I'm sure lots of men who say they are straight engage in oral sex with other men, but if they continue to claim that they are 100% straight, it's only because of some stupid and meaningless cultural stigmas.
I consider myself straight to the bone, and nothing in the world could make me want to suck or get sucked by a dude. The very thought is appalling to me.
Anyway, people should get their jollies however they want and stop being ashamed of it. Who cares if people are straight, gay or bisexual. There's no need for these closet straight men to deny their sexual tendencies.