What you describe doesn't sound like a sensible move from Bethesda's side.
I'd reckon that Bethesda assume that GOG, being a company and a (soon-to-be) competitor, will benefit from being able to offer more free games.
Even if you're able to get Arena and Daggerfall for free elsewhere, being offered handy installers for these famous prequels to ridiculously famous games may bring new customers to GOG.
I'm pretty sure that giving their competitors the right to distribute their games for free is an entirely different matter for Bethesda than giving the games away themselves and allowing them to be distributed by people like you and me.
aluinie: I am happy having them here as they are part of the elder scrolls history and not having them here would be like having one of your body parts missing.
^ This. :D