whoa whoa wait thats some confusing info...how did he die in FO1 (i did see him at that cafe in FO2) but you are telling me a dog that not only looks the same but he has the same name as FO1's in FO3?
Dogmeat in Fallout got killed by a forcefield, Dogmeat in Fallout 2 is an easter egg companion, Fallout 3's dogmeat is a throwback reference to Fallout.
I honestly thought that in Wild Wasteland, he would have been an easter egg companion but I was sad at the loss... He just became a fan service, so maybe it's for the best.