I think we still have to remember that "Frog and Toad" is geared primarily towards kids.
I know it may not be as much the case today - but a lot of the cartoons and books I read when I was a kid dealt with characters of the same sex who were good friends. Never for one second did I ever make the connection that they could be gay no matter how big the overtone was (not that I knew what being gay was back then either).
I believe that if you wanted to, you could find gay overtones in pretty much all of them now -
Bert and Ernie on Sesame Street is the obvious one - and how many rumors were there about Mister Rogers being a closeted homosexual - was it because he wore cartigans? because had a neat house? was friends with a "Mr. McFeely"? or because he had tea parties with puppets in the Land of Make Believe?
Even cartoons for older kids weren't much better. I used to love He-Man and the Masters of the Universe. How many female characters were on the show? I can only think of three (Teela, Evil Lynn and the Sorceress for those of you wondering). The rest of the characters were a band of half naked buff guys in spandex. And G.I. Joe? Come on...you know some of those guys were "Don't Ask, Don't Tell". How many "female" Transformers were there?
I guess at a young age kids are more likely to relate to groups of close friends of the same sex, rather than a mixed group of boys and girls. Maybe because its during the elementary years where most boys and girls find each other "icky".
If Frog and Toad were a male and a female would it make things different? Would sexual overtones go away? I don't think so. Some people wouldn't buy the whole friend thing -- because obviously a man and woman couldn't possibly be that close to one another without a little someting something going on behind closed doors.
I think their relationship can be whatever you want yourself to believe. If you want to believe that they're gay, then the story lends itself to that; of course if you want to believe that they're straight, it lends itself to that too.
Oh well...just my 2 cents worth.
"You pile up enough tomorrows, and you'll find you are left with nothing but a lot of empty yesterdays. I don't know about you, but I'd like to make today worth remembering." --Harold Hill from The Music Man