Just out of curiousity...

Had my tire changed a couple weeks ago, was time for some new skin after 7k on the rear. After it was all done the guy at the dealership (which is the only yamaha dealership around that actually know much about what they are selling) asked me if I rejetted after I switched my exhaust. I have the Cobra slash-cut slip ons on the bike. I told him I didn't change my intake at all, only added the slip ons. He told me a lot of guys make this mistake and he sees bikes come back with burnt up motors from running to lean after changing out the pipes. Basically hes saying that changing the pipes without rejetting is making the bike run lean which makes it run too hot and burns up the motor?

Is there any validity to this statement or is he mistaken? Have run my bike with stage three for over 5k miles and have been running the slashcuts for about 1k never seem to have had a problem with mixture. I have never rejetted or touched the pms going by what I have read here I'm safe, right? Just looking for some peace of mind.