Gtalk did not kill XMPP. Very few people were using XMPP before Gtalk, most people were using AIM, ICQ, MSN, Yahoo Messenger and other proprietary protocols. Gtalk supported XMPP to gain traction as a more open messenger and possibly because they implemented the original version on top of XMPP to get it out the door faster.

Gtalk did pull the plug on XMPP but that didn't really change much.

I don't remember EVER interacting with someone with their own XMPP server. Gtalk had nothing to kill.