I don't agree, but I don't disagree either.... I think that most chins that people buy have good personalities, but again, it depends on the chin. Out of the first four chins that I (still) have, two were pet store chins, and two were from a large well-known rancher. When I got them, I thought they were all very sweet and friendly. Now, years later (my first chin is now 8 yrs old), the two pet store chins have somewhat changed personalities. My first chin, while still friendly, is now super-territorial and will bite when you try to get him out of the cage. My second chin, while friendly at the beginning, we now call her "the part-alligator chin" because there is no touching her or picking her up without thick leather gloves on. Those were my two pet store chins. My two chins from the rancher were sweet when I got them, and are still sweet 6 years later. The one is actually my favorite chin (Toby) because he is just the calmest most complacent chin ever. Loves to be picked up, loves to be held and is just all around great.
The point is, while I think it's fine to say that pet store chins are friendly (I imagine a lot of them are), I don't think I would say that they are more friendly than breeder chins, per se. I've met a decent number of chins, pet store or breeder, and it seems their level of friendliness depends on the chin.
Another case in point - my mother's chinchilla is from a petstore. Seemed sweet when I got her (was a Christmas gift from my dad to mom, I went and picked her out)... she is the freakin devil chin! Omg. This chin HATES me. Sprays me, bites me... loves my mom... refuses cagemates... she is just the devil chin. Not for my mom, but she doesn't like anyone else... but she was sweet at the pet store, or I wouldn't have picked her out.
But then, I've also had some breeder chins come through here... I have one chin here bred by the same rancher (but bought from someone else) who I think would go perfect with my alligator-chin... cause she is just not friendly and barks and has some.... issues. So, I'm going to go with, I think it depends more on the chin.
Not to mention, often pet stores get their chinchillas through wholesalers, but ultimately from those large ranchers....