The Erotic Highway
Dear johnny,
Well, if it's really NEVER, as you say in your post, then it really means that it's been your M.O. until this very day...and why worry about it...if it feels good to you? Does it? We could speculate on various theories, but ultimately, this is the science of doing, not being. So my concrete advice to you is to get your penis sucked over and over again, by whoever you feel is the appropriate person to do it, and then note carefully if anything changes. You know, it's not a sin to get the laying of the hands upon the holy staff to consummate the final act 
It could be that you need that extra vigorous stimulation for the home stretch. There is absolutely nothing unusual with that. But what happens during intravaginal sex? Are you able to ejaculate at some point or do you need to pull out and self-stimulate? And are you wearing a condom at all times, or does it come off at some point?
All these variables, jonny storm. Once again, the best thing to do is to perform the experiment over and over again, change one or two things (the variables)and take careful mental notes, or written, if you prefer. It sounds like a great project. All you need to worry about is if it feels good to you. If it does, do more of it. If it doesn't, do something else. And don't worry about what others say or do. YOU are the main star of this production and that's the only thing that matters.
Happy sucking and fondling,
the Love Goddess