Please correct me if I am wrong, but contrary to your retromags.com (which I like a lot by the way), the owner of the site got in contact with all of the respective copyright owners of the magazines he offers for download to seek for approval to do so. For those magazines, he was unable to identify or get in contact with the person/entity that holds the rights, he will remove them immediately as soon as he receives a complaint from them.
This information can be found in the 'Das Projekt' and 'Neuigkeiten' sections of his site which are in German, so you may have missed them.
The responses from the old publishers have been very positive with the consensus that he is conserving a part of gaming history with his project and many even offered him old issues they had lying around to complete some of his series.
His project is non-profit also and he even puts in his own money to buy old stuff to put online. He is also reliant on donations from personal magazine collections, which I gladly offered myself to help fill gaps in his database.
I deliberately left out Club Nintendo Magazine in my answer to lytron since Nintendo would never give their approval to distribute their IP of course. But all other magazines from lytrons original post except Retro Gamer, which is too recent to even consider, are safe to obtain from kultmags.com in my opinion.