It probably was an AMD processor. Intel came up with the SSE2 instructions and it took a while for AMD to implement them. There was nothing wrong with the AMD's and I preferred them but they just didn't have SSE2.
A few years ago we were trying to install software from a major GIS company. The installation went fine on most machines, but failed on others with no reported errors. I worked with the company to solve the problem and it turned out to be SSE2. They weren't even aware of it. The compiler optimizations used the instructions by default and everything they tested on was Intel. I wound up writing a little assembler program to incorporate into our installation package. It was only a few lines but tried to use a SSE2 instruction. If it failed, we knew the software could not be installed on that machine.
As a user, I have no problem with older machines and operating systems. However, when I put my programmer hat on for my day job, supporting older systems is a pain in the ass. My approach is if our software runs on your Windows 2000 box, great. If it doesn't, you're SOL.