It’s actually a tradition. Joey is on target with this one, as well as Randy. When the comic book heroes transitioned to radio, it had to be visualized totally by voice. The hero couldn’t be seen in his or her super suit, so they had to convey the disguise somehow.
For a great example of this, Listen to one or more of these.
The actor portraying Clark Kent/Superman falsettos his voice while being Clark and lowers it while playing Superman.
FYI: you can download these and many others on iTunes for free. Great when your eyes are tired or for long car or airplane trips. For iTunes put in the search term Botar in the store, or for more, OTR or Old Time Radio.
You also have the good guy/bad guy factor in there as well, often portrayed by voice being lower and higher.
and pete, perhaps it doesn’t, but doesn’t getting kicked in the family jewels alter ones voice a tad? I think blue was taking a bit of illustrative liberty there to emphasize a point