See I am in the same boat. I am finalyl going to have money to spare this tax season and I was going to get a updated 24' iMac. I was incredibly excited that in Feb I could have one, then Apple crapped on my heart and buried my dreams.
Luckily, because I am sick in the head I visited the local Best Buy and was checking out an iMac, and the guy there said if I bought there warranty, that I could come in and just replace it when they upgrade it. I did this with iPod also.
I'd REALLY have to see some proof of that one. You can try and fry a computer whilst making it look like you didn't do anything. However, to think that best buy would take the computer back and give you a new one that isn't the exact same specs, but in fact the newest one, is just ridiculous. Unless it's a full cash refund.
I don't doubt that this is what the salesperson told you, but keep in mind that most sales guys are soulless bastards who just want to get their commission and go home.
I highly doubt best buy would really do something like that. Especially with the economy being in the crapper like it is.
Either way, best buy doesn't even carry the current 3.06ghz 24" iMac on their site, I doubt it's in stores. So best buy is out for me. I'll use the student discount with apple anyways. Saves me more money and I'll just get a mobileme subscription.