predcon: Not this.
My notion was that GoG would pay a contract fee to the developer of Xpadder for a "GoG exclusive" version, the same way Western Digital bundles a specific version of Acronis TrueDrive that only works with WD hard disks. GoG has to have enough money by now that bundling such an "exclusive" version of the software (embedded within each game) would only raise each game's price by three or four dollars.
It still makes little sense; even if you assume it would raise the price just by 1 dollar, as the poster above pointed out, a full licence directly from the developer cost 10 bucks TOTAL, and will cover EVERY game you own on GOG and elsewhere...
Also, people would expect to have some kind of support for that software from GOG, since they'll be acting as a distributor, and that would cause some added headaches, with very little benefits in exchange