I managed to find an explaination for corny earlier and yep, Faldage and Websafe - you were spot on!
(about the connection with the supposedly 'simple-minded coutry folk' thingy.) It said this particular meaning was a 20th century development. I'd always thought it had something to do with corned beef or something...
Nothing on cheesy, but on thinking about the phrase 'cheesy grin', could it have something to do with over-posed photography etc?
I enjoyed the suggestion of a possible Dr Seuss and nerd connection. I think this is supposed to be the origional bit it was in:
"I'll sail to Ka-Troo And Bring Back an It-Kutch, a Preep and a Proo, A Nerkle, a Nerd, and a Seersucker, too!"

I guess now only one question remains: what's a Seer, and how do you suck it??