This is my understanding as well. To give this some perspective with a modern-day analogy,
heart surgery, while anyone is welcomed to learn it,
but you'll first have to go through many levels of teachings to get it,
and classes in it are not open to just anyone who walks in through the door.
This is because without establishing the correct context for understanding it,
you won't properly understand it at all.
I don't know of any lama who isn't glad to share what he knows
provided the student is really ready to learn it.
This is a helpful analogy as far as it goes.
There was a time however, in the United States, when anyone could walk in the door and receive whatever empowerment was being given, no questions asked and no instruction given either. Lama flies in, and then flies out. Finished.
i will say this quite openly, i had never even heard the word samaya, let alone understood the concept, until i started participating on e-sangha in 2007 and by that time i had received many empowerments, including having been to India and Nepal. I am assuming now that situation existed because i was never a part of the "in group" and hence privy to "secrets".
"Secrets" exist and are in kept intact for many reasons. Some of those reasons are neurotic. Some are useful. Americans especially tend to be very open naturally and also very neurotic. (I am American, btw). We talk about everything in America. Its taken me quite awhile to understand that other cultures are not quite so open and also less neurotic.
That is the relationship that needs to be studied i think - the cultural interplay of secrecy, neurosis and openness.