I'd say that's because generally everything is faster on Pentium 4...
How fast something opens is always relative to everything else, and whether you've used slower computers in the past and so it now seems lightning fast, etc.
[For me on a Pentium III with 650MHz, the average window will take a couple of seconds to open, while YaST window about 10 / 15 seconds. Prob. faster for everyone else.]