I think it was another "point of difference" that Apple had over x86, something that they could use to market against all the x86 clones, because the OS really wasn't something to harp on about at the time.
And they did that with all the "benchmarks" that Apple chose to prove that per mhz the PPC could beat a pentium. Whether the benchmarks truthfully represented performance differences in the real world for the average user or were contrived tests that worked better on PPC architecture is another argument. Jobs just had to run a few photoshop filters that worked faster on PPC to prove his point to the masses that PPCwas indeed faster. Nowdays the hardware point of difference is largely aesthetic, which works better than ever to get people to get a mac.
