Nice to see such ancient threads revivified! As to why 4 & 20, the answer may be implied in a common medieval/renaissance riddle form which crops up when Lear's Fool is trying, unsuccessfully becoz he knows it, to cheer up the poor old King [King Lear I v] -

"Fool: ... The reason why the seven stars are no moe than seven is a pretty reason.
Lear: Because they are not eight.
Fool: Yes indeed. Thou wouldst make a good Fool."

[7 also a mystic much-quoted-in-folklore #, like 24; & thus, similarly, liable to be arbitrarily cited]