Freee- comments is authority on its own
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but added ideas be gleened by seeing how the gates were designed. I don't think there is a reference saying explicitly "we used 5V because ..."
There is a chapter in Horowitz & Hill online you cause use as a reference, I think its on interfacing digital to analog; it describes gates from different technologies and why they need their specific Vcc and how to mix and match them.
Folks may not realize TTL was patented, so it had specific design constraints. Consider V
oh ~ Vcc-2, so to guarantee a switching transition at >2.5V there is very little room should Vcc drop below 5V.
On the top end of Vcc, BV
ebo makes a good case.
Any citations guys? I did read that thread and the Wikipedia article but was hoping could find a more authoritative source. Thanks @satuation and @ptricks!