I agree that by nature, Guinea Pigs would not be petted or stroked etc by humans, nor would any other animal. BUT I also agree that it is important they are used to it enough, not to be scared or stressed out when you do need to handle them - say if they hurt themselves and needed to be helped or, I dunno, their nails needed clipping or vet visits.
I think it depends on the pig as well. I have 14. My 4 granddaughter-pigs all hate being handled. They have been picked up and stroked since birth but they hate it. My grandson-pig (in avatar) loves, loves, loves it! He comes up to the bars and waits to be stroked all over, picked up, carried around sat on my lap and played with. He only asks to go back when he needs a wee, otherwise, he'd be on you all evening!
My 3 piggy-sons all like being fussed as well but not picked up so much. 4 of my piggy-daughters again, don't like being picked up but love being fussed over once they're out on your lap and the other 2 are quite anti-social when it comes to hooman attention. I don't think their previous owners were very cuddly with them at all.
Different personalities, I guess! Same goes for all animals I think, just like us hoomans/ slaves.