If he found a secret way to make ISOs it should work on his PS3 also, he has probably never updated the firmware in his BDS300, and thats the reason it works
There is no 'secret' way to make an ISO which will put the ROM mark on a Blu-ray disc from what I've read it's hard encoded onto a part of the disc that you can't write to
PowerDVD plays BD+ backup copys, (without AnyDVD loaded) so why should not the BDS300 be able to play this to, if you update the firmware of the BDS300 to the latest it will not play them anymore, it`s that simple! maybe even the PS3 can play those with an old firmware? but as far as I know you can`t downgrade the firmware on the PS3, or can you???