No, they didn't.

It's all described here:

It's talking about Vista but the principle is the same for XP. Basically, the key you discovered using Everest (et al.) was a key used during OEM install that produces a PC that doesn't have to be activated.

'Cos that would be a big pain for PC manufacturers and big IT departments

More info is on:

Personally I don't know why Microsoft bother as WGA cracks and by-pass techniques are all over the web.