I think it's like Apple cables: for some they're frayed in a month, others still have perfectly serviceable 30-pin cables that they've used daily. Personally, I wear Unbound merino t-shirts and underwear, and they last for years.
(I'm also convinced that front-loading washers make clothes last longer because they don't literally beat your clothes to death.)
We haven’t utilized double-blind tests at our house or anything, but definitely makes a difference in clothing longevity for us. Popular consensus seems to agree, FWIW.
(I'm also convinced that front-loading washers make clothes last longer because they don't literally beat your clothes to death.)