You bring up an interesting point. However, my impression from communicating with these people, and reading what they have to say about what they do is that they actually have a very good understanding on whats going on inside of your typical ad/da interface.
but dont take my word for it, you should go ahead and ask them yourself why they have chosen to put video opamps in there.
Or you can read this thread over at unicornation which adresses most of your questions (you may have to register though):
http://www.unicornation.com/phpBB2/v...hlight=#100408
Have a nice day!
/J