Do all amplifiers sound the same?

Some time ago the now defunct stereo review had an interesting article
on blind a/b tests between different amplifiers - I saw a reprint
here;

http://bruce.coppola.name/audio/Amp_Sound.pdf

After a hiatus of many years I am now putting together a system and
every one I talk to tells me there is a difference between amplifier
sounds. I am sceptical and in a recent audition could not tell a Creek
EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
source).

Has any more work been done on this subject, esp. blind a/b tests?

Steve