"According to the data sheet for the AT89C51RD2 (and 'ED2) 0FC00H is the entry point for the bootloader."

You've (quite understandably) read more into the datasheet than actually exists. It only says that the SBV (Software Boot Vector) should be set to 0xFC to enter the manufacturer's bootloader on reset, not that the bootloader actually lies at 0xFC00. This is apparently for historical reasons, ie the Temic parts were like that and they forgot to change it.

"I also tried the AT89C51ED2 and AT89C51RB2 and both worked as described."

As described where, exactly? The datasheet for the RD2 and ED2 is the same and has a quite astonishing 'errors per page' count, particularly in the areas that describe the bootloader and API calls.

"It also makes references to the old Temic T89... parts."

Yes, they are obviously cut and paste jobs. The bits left over from Temic are well written (although often incorrect as the new devices are different), the new bits appear to be written by someone who either doesn't speak English or isn't familiar with the parts.