Not necessarily. For instance, the PowerMac G5 and iMac G5 have powerful IBM PowerPC processors, better than any AMD out there, and more powerful than lots of Intel chips. And in terms of software, Macs are unrivalled, with the new Mac OS X v10.4 Tiger, there is no operating system like it.
Thats their cpu, not the rest of their hardware. You cant pop a brand spanking new graphics card hot off the line into a laptop.
But you can pop a new graphics card into a Power Mac, which can make it better than a PC, and most Power Macs come with high end video cards anyway.