I think that I agree with you but, like Tess said, I think that they can at least be slightly interchangeable. I'm an Administrative Assistant (my original title was Administrative Assistant to the Executive Director until she resigned last year) and I pretty much fall into what you said about that category. However, when the ED was around, I would also act as her personal assistant and do some executive assistant type stuff. Now that she's gone (I actually got laid off when she resigned because I "was hired to be her assistant and she's not here, so we must not need her" (use a deep haughty BoD type voice when saying that...lol) and I'm back, I still call myself and Administrative Assistant because I do all of that, but I'm also acting as the Account Manager (without the title and pay

), so I think in today's business arena it pays NOT to be a "one trick pony" and, even though you may have a certain title, not get yourself tied into that stereotype or roll.
Secretary...hmmmm I don't use that word very much anymore. My mom was a secretary; I'm an administrative assistant. Today, I think their pretty much the same thing. An Admin Assistant is just a more modern term. Also, when I think of what I thought secretarys were a few years ago, I would have put them more towards the top of the ladder if not the equivalent to an Executive Assistant. But that could be because I used to think my mom was very important and had the greatest job in the world when I was little (not that she's not important now, but you know what I mean).