For the record
intel has at least 8 sockets
P3 and older celeron (socket 370) (yes you can still buy these new)
Pentium M (modified socket 478)
P4 (socket 423,478 and lga775)
Xeon (socket 603 and 604)
Itanium/Itanium2. (don't know if they both use the same interface or not to tell you the truth)
AMD only has 4 sockets.
Athlon 32 bit series (socket A)
Athlon 64 bit series (socket 940,939, and 754)
There's really no way to unify socket design, it'd be like every car in the world having to use the same size wheels and tires.
Don't forget about Socket 423 for the P4...
I thought about that, but you can't buy them new anymore as far as I know, but I added it to the list none the same