The reasoning here is simple, bitset disks lie!!!!!!!!!! Thats a good thing though. Dvd-r has been around longer, and that is the only reason it was considered more compatible. The disk said, I'm a dvd-r, the player said, I can play dvd-r, let me try to read you. You had to have a newer player for +r, and if you did, it would do the same. When you bitset a dvd+r, it does not identify itself as a +r. It identifys itself as a dvd-rom (it lies).
Every dvd player made reads dvd-rom disks (or they wouldn't be dvd player). It is possible that even if it tries, it cannot read the disk, but with a bitset +r, it sees it as a normal pressed dvd-rom, and at leat tries to read it. that's why bitset+r is the most compatible.