wpegg: So you're not keen for your bank to have https? Signing installers is a similar business, though a little less easy to get caught in a trap. People that are new to GOG don't know if they are legit, lets face it, at times it seems a bit too good to be true. A digital cert helps some people feel secure just as much as that padlock.
PhoenixWright: I see what you're saying and you raise a good point, but isn't HTTPS a little different, based on the fact that it is actually providing literal security protocols in addition to the "signing" aspect?
Yes, https is there because you don't trust your connection between you and your target, digital signing is there because you don't trust your relationship between you and the provider. Because https is defending against a third party it has a proper implementation, but the end user doesn't usually know that. They just know padlock - it's safe.
EDIT: in fact I'm wrong, both are doing the same thing. There's someone you're not sure you can trust, be it the connection, or the provider of the software. A CA provides a confirmation that what you're doing is safe. Either by providing a key between you and the target to communicate with, or a key between you and them to say the provider is safe. Both times, it's the CA telling you that you can trust this.