-cerberus-: What's the purpose of Connect then if not to migrate games to a DRM-free platform?
JAAHAS: To get more potential new customers to sign up here, it is just a marketing stunt which may or may not have cost a fortune to GOG, depending on whether the publishers agreed to allow the Steam licenses be duplicated to GOG licenses for free or if GOG had to pay them a more or less discounted price for each new license.
I *highly* doubt it ever cost GOG anything to do that. This is basically an extension of what was a common practice with Steam keys before. There were tons of developers providing Steam keys for games people owned on their own (developer) websites for instance.
The big difference here was that GOG was able to automate that process because Steam has an API that can connect 'ownership' of a certain title to a specific person(account).