There's no games that I know of on A500 that need fast ram. You can't add fastram to A500 trapdoor, so in that way 500 and 600 is the same.
He means Slow RAM really (trapdoor 512K in the A500), but it was known as Fast RAM because it wasn't Chip RAM. As OP stated, there were a few crappy games that only work with Slow RAM due to the programmers making assumptions about where the extra 512K actually is, address wise. For instance, if the extra 512K was configured as Chip RAM the game wouldn't work despite 1MB of RAM being available. The programmers are to blame, certainly not Commodore!
I suppose by the time the A600 was released, those games were old anyway and no-one were much interested in them, and programmers had learned from their mistakes. That Slow RAM was useless anyway by the time the A500+ and A600 were released because the Chip RAM could be expanded to 2MB via the trapdoor, and Chip RAM was what the people wanted (more sound, graphics, more open screens etc.)
