Maybe John Smiths is a bit simple and characterless and not to everyone's taste, but it does have quite a strong and distinctive flavour.
Many years ago, I entered an informal homebrew competition where the competitors judged the beer by blind tasting (and these were serious beer drinkers who knew what they liked). Anyway, one guy whose brew hadn't turned out so well substituted some John Smiths bitter as a joke. The tragedy was - it won!
Even once we'd been told, we still couldn't believe it was John Smiths - but it was.
Well, at least he owned up, so we could pick a true winner. It wasn't that the other beers were bad. It's just that when you've tasted loads of different beers your palette can get a bit tired. Something with a relatively simple but strong taste - like John Smiths - then stands out from the crowd. Sometimes I've noticed this effect at beerfests too - the prize ale isn't necessarily one you'd want to drink at home, but it has that edge that lets it cut through the crowd and stand out.
I don't think that'd work with Tetleys, mind. The week-old wet flannel taste would surely mark it out.