Because it is not 62, it is 58:

https://en.bitcoin.it/wiki/Base58Check_encoding

'0' 'O' 'I' and 'l' are not used, 62 - 4 = 58.

So, in fact, his equation is in error.  We only use 24 of the captital letters so 24³³/58³³ = (24/58)³³.

I am surprised no one else (including me) caught that the first time around.

It was interesting to read my OP in this old thread.  Man, all I can say is what a noob I was back then