Faster clock doesn't ALWAYS waste more battery power. Take my laptop for example. It had a C2D 1.6GHz and while taking notes in class the fans would come on every few minutes for about 30 seconds and then cut off. Not too bad, I got about 2.5-3 hours to a charge. The processor would almost never leave idle speed of 1GHz during this time.
I then upgraded to a C2D 2.16GHz and I can take notes the entire class with the fans not coming on even once. The 2.16 idles at 1GHz much easier than the 1.66 did. It even has a lower dissipation rating than the 1.66 did and I've now got about 3.5 hours on a charge for that battery now. Not to mention double the cache.
You raise excellent points about clock speed and I believe the situation I brought up is an exception. A P4M-1.5 will probably last twice what a P4M-2.2 does on the same battery.
Oh, and V8s are fun.

At least, that's why I drive one.