They made the Limited Edition ones for the 2 very common cars they were selling for: Civic and Integra. So they just make more GC's for these cars and sell them with the "Limited Edition" tag line at a cheaper price.

As for the spring rates, they're the same, but I'm pretty sure that you can't send them away to get the spring rates changed if you ever wanted to. So for most people, that's really not a problem.