It does help don't get me wrong, remember the old days when an Athlon at like 1.8ghz would be quicker than an Intel at 3ghz, then Intel bought out the core 2 duo's and amd were nowhere to be seen? It's down to how the cpu is able to process the data and the route it has to take and the intruction sets it uses, when you get a cpu of the same architecture ie. An i5 2.4 ghz v 2.8ghz then of course the higher clock speed will be the quicker cpu but different cpus handle data more efficiently than others 
If that wasn't the case then we could say that an old 1.8ghz sempron would be the same speed as a newer am2 sempron at the same clock speed
If that wasn't the case then we could say that an old 1.8ghz sempron would be the same speed as a newer am2 sempron at the same clock speed