No, the feat and the enchantment don't stack.
The whole "realism" notion's certainly highly subjective. After all, what is a "crit" exactly? What, any time I'm not critting, the blow is just a mere flesh wound--regardless of how much damage I do, or even if I kill the bugger?? Damage involves at least one die roll (for the weapon), and rolling maximum on that roll can just as easily be called a "critical" blow. And while one blow that does 50 points of damage to a dragon might be shrugged off, it may well be killed instantly by a blow that does only, say, 15 points of damage (as long as they're dragon's HP are low enough). Most decidedly, something that kills you instantly has harmed you critcally.
Ask yourself a more relevant question: what purpose are crticals supposed serve in the game--or more specifically, in
your game)? If a critical is supposed to occasionally inject some random, unpredictable excitement into combat, then its seems reasonable to place some limitations on how much can be done to improve a weapon's chance of striking a critcial. If a critical is just another element for building a smackdown character, then don't bar that hold.
I just house rule it in my games that they stack. If you're the DM, just do the same. If you're not, talk to the DM and present your reasons for letting them stack (reminding him that prior to 3.5 they did stack and there's not been a valid reason since why they shouldn't) and maybe he'll go along with it.
Perhaps, or maybe he'll pat you on the back and say "you know, there's a difference between a reason that's not valid and one you simply don't agree with".
