The problem is that withholding sex to get a marriage commitment is not a sound strategy for women because too many other women provide sex without the commitment.
A guy told me once a story that during his courtship with a chaste woman, he found himself in an encounter with an attractive blonde. She agreed to go to bed with him and they got naked together whereupon she began puking all over the sheets. That, of course, ruined the moment.
He confided years later that, had the sex been good he probably would have dumped the girlfriend and began dating the blonde. Instead, he married the chaste girlfriend who later cheated on him with a minor and then sued him for divorce (but that's another story...).
The point being, I think there is more pressure on women to have sex before commitment than use withholding sex to get a commitment. Many know they risk losing the guy if they say no too long.
That's probably true in this day and age. I don't think badgering a woman for sex is right, nor do I think it's right to withhold sex from a man for the purpose of inducing him to commit.
If a couple can't agree on when the relationship becomes sexual, they should probably end the relationship. Trying to force one to bend to the other's will is unfair, creates resentment, and probably indicates much deeper differences that will continually plague a continued relationship.