Your argument fails for one reason. Costco invests a lot of money in TP research and manufacturing. I'm not joking. The CEO has stated that there are a few key products that Costco has taken seriously for vertical integration....they start with the manufacturing process and take it all the way to the consumer. They try to get people to continue membership based on those key products...
If you were using some discount product with 1-ply sheets that tear unexpectedly where the sheets are not perforated, it would make a bigger difference.
TP is a lot like fabric softener or detergent. People select it based on a combination of price, perceived value, and perceived quality....after using the product, they will either continue use or search for a new product if it didn't meet their standards.
I always wonder though if someone wasn't truly happy with their TP if they would continue use of the roll or mutter, "I wouldn't wipe my ass with this stuff" and throw it away.