Why limit your program arbitrarily? If it's a performance issue, then let the program benchmark the system, and decide on settings, or whether or not it will run.
What's next? Checking L2/L3 cache sizes, and deciding not to run, if you don't have enough cache memory?
More cores, are just a means to an end - higher overall performance. They're not an absolute requirement.
And if Intel comes out with a 10-12Ghz single-core with HT in the next five years, what are you going to do? It probably would have enough performance to run this game, but ... it won't play. Arbitrarily locked out.
There's a big difference, between "it works, but it doesn't perform well unless you use it with a (current) quad-core CPU", and "No, it won't ever work, it's just ... arbitrarily locked out, due to the technology available at the time that the game was written".
Again, it's either lazy devs, or some sort of Intel-sponsored conspiracy to sell quad-cores to gamers. Which wouldn't really surprise me. (Reminds me of tessellation and NVidia video cards.)