Great logic, so if something is old it must therefore be incredibly easy to emulate? I mean after a certain period the rom just unlocks all of it's secrets ready for emulation. If you knew anything about programming, you'd have come to the conclusion that you have just spouted out a lot of nonsense
If you knew what it took to get something like Banjo Tooie working for example, I think you'd be in awe as to the level of skill needed to find out things about these games. If the documentation was available on these games, or was hackable - then it would have been emulated already. At the moment the games are a locked safe (only a very few in amount too), a programmer needs to find the correct method to 'crack it open'.
Nightmare Creatures like Dezamon3D is just one of those games that may use a slightly different boot code, or it may have required something that would have meant changing a lot of other stuff for it to work. I would suggest that you are nitpicking though.
If you don't like the emulator Death Rin VR, may I humbly suggest you do not use it. Better still learn to program then come back and tell us how sorry you are for judging the programmers ability and desire to emulate the N64.