I think that what Peter is looking into is a "distribution" copyright:

the programs included in the SLS distribution will naturally have the

GPL apply to them *singly*, but the SLS distribution as a *package*

would be copyrighted by SLS to some degree, so that some random person

couldn't just take the SLS setup and sell it as-is.  I don't know how

well this works under copyright law, but I think it's possible (and it

wouldn't be against the GPL).  There are probably net.lawers out there

that know better about compilation copyrights or whatever their legal

status is (similar to anthologies when it comes to books - the stories

in a anthology are under different copyrights, but the "package" also

has a copyright to protect it). 
As to whether it's a good idea or not is another matter: I personally

think Peter (and others like Yggdrasil) have good reason to do something

like this.  The GPL was meant to make the sources free, but one aspect

of the GPL is also that people like Peter and Adam should be able to

make money off them by making value-added packages with support and

other services.  Putting the SLS under some kind of copyright would not

hinder others from using the programs therein, it would just mean that

Peter could try to have some kind of "quality-assurance" of the

different packages that go under the name SLS - something that should be

good for everybody. 
                Linus