I can have sex without BDSM, but it's boring. It's like being hungry and eating a bag of chips and drinking a soda. Does it taste semi-decent? Yes. Does it fill me up? (no pun intended, i swear) Absolutely not.
I have a much more difficult time achieving orgasm if there isn't any power play or BDSM involved. It can be either physical or psychological, but it has to be there, otherwise there's nothing to push me over the peak.
Interestingly enough, my first orgasm (a looong time after I'd started having sex) was from my partner giving me oral sex, but it was a very submissive and vulnerable act for me. I felt embarrassed for anyone to see me naked and I was especially self conscious about my vagina/anal area. He really wanted to do it, but it was a struggle for me to say yes. Even from my first orgasm, my pleasure has been completely tied up in submission.