Funny, isn't it? People's voices have got a quality that's uniquely theirs. Everybody's got voiceprints. Quinn's voice is recognisable anywhere, and not just because of the accent.
Just today, I discovered that there is apparently a long-standing debate as to who sings the echoey “aah-aah” bit on “A Day in the Life” from Sergeant Pepper (just after the central section by Paul that starts with “woke up, fell out of bed…”). It's so obviously John that it had never occurred to me that people could hear it any other way. Paul just couldn't get that eerie quality into his voice, which corresponds to the way John sings the other sections.
Quinn's “stupendous!” has got a gravelly sound to it that is utterly unlike Tyler's nasal voice.