It was my understanding that software (software DVD players, operating systems, etc.) could implement region restrictions, but are under no technical obligation to do so. Many might partner or enter into agreements which might require certain behaviors of the software (like region checking and enforcement).
It seems that 32-bit and 64-bit versions of Windows have a region enforcement system. Other operating systems like Linux and DOS do not seem to implement region restrictions on DVD media. Further their are software players for 32-bit and 64-bit Windows that disregard the Windows region setting and also claim to be able to play region coded DVDs of a region setting different than what is represented in many optical drive's RPC-2 firmware.
In my opinion, RPC-1 should always be preferred to RPC-2. The software interference, should it exist, may be dealt with (rather easily). RPC-1 is also truly the only acceptable means for being region free (the auto reset firmwares will require powering down the DVD drive RPC-2 auto-rest region changes have been used up).
On a side note, it would be good it the Windows 2000/XP/Server 2003 DVD region checking/enforcement system could be patched to disable it.