4 cores isn't as expensive as most people believe. Even if they're going to be idle I'm going to pick a slower quad core over a faster dual core for general computing. $150-180 gets your foot in the door for a quad core processor.You are correct, the $2500 isn't a lot to ask for what you get, but what you get may be more than you need. Most users don't need the 4-8 cores of a Mac Pro with Xeon chips and 32GB of possible RAM.
Many just need the 4 cores of a regular desktop chip, and expandable HDD, PCI and GPUs.