I'm just speculating here...
Thing is, you might be in luck. Apple's Core Duo stock ran out ages ago. About the only places you can still buy CD macs are: refurbished (from Apple), third party stores selling used stuff or third party stores selling them at full price as if they were the latest version.
Given your, I'd say, pretty bad experience with Apple, they wouldn't really risk making it worse by not giving you a brand-new C2D computer. Fact is, you deserve it, and if you don't get the quality of customer service you deserve, they assume you'll (and everyone else who hasn't had a reasonable experience with them) probably tell other people what happened. I'm not saying you're greedy, but Apple was voted the company with the best customer care, which means they want to keep their clients happy, and if they want to do that, it's perfectly reasonable on their part that they give you a C2D MacBook.
Hope things work out great for you.