As far as we know, that is correct. I do remember Sirius saying that he didn't think Regulus was important enough to be killed by Voldermort himself. I want to say that Sirius said that something frightened Regulus, but by then it was too late to get out and that is why he was killed. I don't have my books handy, so I will have to check it out a little later.
I never leave home without them:
"From what I found out after he died, he got in so far, then panicked abut what he was being asked to do and tried to back out. Well, you just don't hand in your resignation to Voldemort."
Here's a thought... was Regulus asked to do the same thing Draco was asked to do? Hmmmm?