I think what Gavin is trying to say (sorry if I am putting words in your mouth) is that it really doesn't matter who made the mistake, someone has to make it right, assure you that its not going to be an issue, make sure the mistake doesn't happen in the first place, and in an ideal world, that person should be the person you spent all the face-time with...the salesperson.
RichardL is correct that in most all dealerships there is this back and forth between sales person, finance manager, etc, and each has their own responsibilities.
Regardless, a mistake was made. The mistake needs to be fixed.
Personally, I LOATHE dealing with all the various people I have to deal with when buying a new car. I actually think a deliberate part of the problem dynamic is the fact that there is no longer "one guy" you buy a car from, but there are several. Because of this dynamic there is always finger-pointing, this adversarial dynamic ("I would like to give you this deal, but my finance guy won't let me"), and the opportunity for mistakes to be made/overlooked.
This is why the last three new cars I have bought I did my test drives, got my pricing from Edmunds, got my financing from eLoans, got my rebate info and dealer invoice info over the phone/fax, and then made my FIRST and FINAL offer over the phone. Dealt with one person and told that person that I didn't want to talk with anyone else, and when we agreed to a price I told them to "have all the paperwork and people ready...you have 30 minutes to finalize the deal and I will be driving away from the lot in exactly 30 minutes from the time I walk in the door, either in my old car or a new one!"
Yeah, I'm not a favorite for car dealers, but if the truth really is what they say, that they only make a few hundred dollars on each car sold, then I'm not a time-sucking tire kicker either.
TJR