Like people have said it's just friendly rivalry.

Most people know that if you want to go fast either will be up to the task.

Engineering/Approval is still the biggest deciding factor in most cases. I know I tried to find away around the original tare mass in kg x 2.5 rule that exists in NSW and ACT. Most people use the commercial vehicle loophole when putting in SR20's, but I went CA18 just to be 100% legal (in my state).

I still wish the rules were more lenient and you could have more freedom to make crazy street cars