Sure, they can't guarantee speed with a particular service, but they can guarantee width and reliability of my pipe. Believe me, back then I was downloading so much crap that my internet was stuffed full at all times. I'd notice any dip in service.

And when I was on ADSL, I did notice those dips. A lot of them. With FTTH, they went away.

There's a difference between "they guaranteed it to be that 100.000000% of the time" and "in practice, it actually was that the entire time". The latter can definitely be true.