This discussion reminds me of my original post, a question of 'buddhist fundamentalism' because, if we are talking about why one tradition is incompatible with another, and someone brings up, "Well, Buddha said this...." there is a sort of irony, aside from the fact that nobody knows exactly what the Buddha said, and what the context of that very moment was on that particular day some 2500 years ago. This is what I see as 'fundamentalism'.
The irony is this:
1. If what the Buddha taught, if the dharma he explained can bring a person to the same realization that he had (and you can call it nirvana or end of samsara or liberation from dukkha or enlightenment or peppermint or any word you want, I think I'll use 'realization' here) then his teachings are valid. If they can't a person to the same realization, then they are essentially useless, or at least not worth disagreeing over.
2. This can only be determined if in fact, by following his teachings, others have attained 'realization' . Most buddhists believe that there are others who have attained 'realization' in these 2500 years, whether they be roshis, ajahns, rinpoches or whatever. If not, then again, these disagreements would not be worth the effort.
3. If (we assume that) 'realization' is 'realization' , meaning that it is essentially one 'realization' and thus the same for anyone who attains it, then whatever is taught or transmitted
(through refuge, lay vows, vinaya, precepts, empowerments, blessings and cosmic sneezes)
are just as valid
(if received from a tradition which has been able to effectively preserve and replicate this 'realization')
--as if the Buddha had given them himself. It's like a vaccine: If it really works, then any licensed doctor can administer it.
4. If we assert that only those words which we believe were spoken by the Buddha are the only valid teachings, then aren't we essentially denying that anyone else has ever attained the Buddha's 'realization' ?
Unless someone might have an allergic reaction to taking vows or precepts, I think they should be given to those who want them, and let them get on with the business of keeping them.
Let me give you an example that may help you to understand. Imagine you want to go from A to B. There are several paths to get from one point to another.
One goes through a plane desert and takes longer. Another goes through a dense forest and it's a little faster. The last one is a shortcut that goes through high freezing mountains and it's the fastest of them all.
Fundamentalism would be saying that only going through the forest (or any other of the presented routes) takes you from A to B. Fundamentalism would also be saying that traversing the desert would be the best path for everyone. Fundamentalism would also be saying that for all people it's faster going through the mountains.
All these paths take you from A to B; not everyone deals well with extreme heat; not everyone can climb mountains. So, the best path is the one that takes you, with all your strengths and weaknesses, faster from A to B.
Now, A is samsara and B is Nirvana, as you figured already. The different routes represent the different turnings of the wheel of Dharma or different approaches to the Buddhadharma in general (lay practitioner vs ordained). Each person has it's own karma and that is what allows choosing which path is best. Let's assume I'm not very athletic. Perhaps going through a plane is easier. If I think, "well, but the mountain route is faster" and I decide to go there, I may get stuck in a very tricky situation. It may take many lives for me to get out of that mountain, more than would take if I had decided crossing the desert planes.
Now, let's assume I decide to cross the mountain. There's a lot of gear I need and surely that gear is not the same I would use to cross the forest or the planes. Saying that any gear will do, since all paths lead from A to B is pretty dumb. So, Buddha and subsequent masters taught many things, but we can't mix them without skill and expect them to work. If you are a monk, you can't keep your vows and practice karmamudra. If you practice Dzogchen, having a sutric approach will hinder your path. These are just examples. Each path has its methods and these things, even if having some flexibility, aren't all interchangeable.
So if your capacities are best suited to cross the forest you shouldn't go through the mountains equipped with desert gear. Do you get what I'm saying?