To start with, I see no reason why someone wouldn't generate PGP keys with two different pieces of software. Especially if one was run under Windows and one under a variant of Linux.
Usually people take great pains to sync up their PGP keys across all their machines if they plan on actually using them. Otherwise if they received an encrypted file what should they do? Take the file to each computer and keep running gpg until they got to one that decrypted properly? Lol.
Besides, even if 2 keys were owned by the same person using the same friendly name for both is pretty retarded.