Do you really find this to be true? I moved from a 400 MHz Pismo (G3) to a 1.33 GHz G4 Powerbook and I noticed a difference in web browsing. They were both running the same version of OS X at the time of the switch, and the same version of Safari. Yet I found that web pages loaded and rendered at least twice as fast, and with java applets the difference was even more pronounced. Scrolling and searching are much faster in the new Powerbook, too.
I'd say the Pismo is adequate for surfing, but to say it is essentially the same as a faster machine is, in my experience, misleading.