But if they did that, what would happen if it was run on a 32 bit Athlon or PIII?
Maybe extend the check to support Athlon64s, but removing it altogether would be "really dumb" as you put it.
Also, I doubt intel would do that just yet, the P4 is its main plug in the high-end market. Unless the GNU project come up with an equally performing compiler (it may just happen in the next few point releases i.e. 3.4/3.5-4.0) Athlon64s aren't going to be directly supported by the intel compiler.