The problem (and D&D sums it up perfectly) is that Feudalism requires a few rich nobles controlling 1,000s of poor, uneducated peons. To get a truly Feudal feeling, you'd have to remove the whole "take their stuff" part out of the game.
Think. A knight is in the service of his lord. He makes a few successful campaigns. He is rewarded with land and a keep, plate armor (a small fortune) a noble steed (perhaps from the King's steed's breeding stock!) and the opportunity to marry another noble's daughter.
However, what out of that does he "own?" The land? Nope. The king owns that and he can give it any other knight whom he deems "fitter". The armor? Insofar as that can't be resold, but I'm sure the king, if sufficiently annoyed, would see that reclaimed for its steel. The horse? Horses are a burden to keep up without grooms and land. The wife? Legally yes, but another mouth to feed (and more, if he's had children) is no consolation when you having nothing else. And the wife could always seek shelter with her family or in a convent. At the end of the day, he has all he has because his king "likes" him and has given him these gifts "on loan".
D&D doesn't work like that. You kill an orc, you have his 100 silver pieces. You gather enough silver (and kill enough orcs) you buy your own armor. You buy your own horse. You settle your own land (and attract followers, pre-3e) and you marry whoever you damn-well please. And if the king doesn't like it, he has nothing to threaten you with except your death or the destruction of all that you've bought with blood and orc-silver. And as we all know, most people will fight to the death to defend their lives, loves, and property. After killing 1,000s of orcs, what a few royal guards? Or Royals themselves?
D&D is venture-capitalism with democratic overtones and a dollop of egalitarianism masquerading around as late-medieval European feudalism. Trying to make it anything else is lipstick on a pig.