Men and women think differently; this is a given. We view sex differently, obviously, but I'm not just talking about the emotional pleasure vs physical pleasure realm.

When you first start dating someone, do you think about how far you would eventually like to go with him/her?
Statistically, men say no. Surprisingly, the men don't see themselves as the one with the sexual power. They figure that the woman will call the shots (and the men are almost always ready to comply!) One may choose to refer to this as "Walking-Penis Syndrome".
On the other hand, women (statistically) generally know about how far they are willing to go with the person they are dating. They have a line drawn in their head and, if thinking rationally, don't cross it. (Always subject to change in the heat of the moment or when drunk.)

But then we come to the point where communication is the key.

Take this situation for example:
A man and a woman are seeing each other. (They really like each other in fact!) Ok, so they're making out or hooking up or however you want to put it and they proceed to have oral sex. At this point, most men assume that they will be getting laid tonight. . .it's only natural. Oral sex is the gateway to intercourse, right? Not so fast, killer. . .don't start making assumptions.
Let's flip to the woman's point of view. . .
Oral sex may be the pre-existing limit in her mind. I think there is a huge difference in the way that women and men view oral sex vs sex. Maybe to a man, coming is coming, any sex is sex. . .I don't know, I'm not a man. But there seems to be a greater emotional link (by women) to actual intercourse, and a far greater physical link to oral sex. (duh!)
Anyway, the point is that oral sex does not mean that intercourse is the next acceptable thing. Of course it can be!, but don't assume that yes to one thing means yes to the other.

I find this fine line very interesting. . .Even though the man may have every intention of letting the woman call the shots, he may just assume that consensual oral sex means that she gave the big OK.

It's apples and oranges

. . .and oral sex