First of all, I feel it's important to point out that Resident Evil, as a series, has never billed itself as "zombie games." It bills itself as "Survival Horror," and used zombies as the incarnation of horror in its first several titles.
So the premise that the recent games are somehow betraying what the games are meant to be is a flawed one. So long as you remain in control of a character in a desperate, life-threatening situation, have to scrounge for ammo and fight for every inch to stay alive throughout the storyline, you remain a player of a Survival Horror genre game. Resident Evil 4 and 5 are, I don't think it can be argued, stock-and-standard examples of just that, as are their predecessors.
Secondly, evolution is a way of life (and of art, which mimics it), and I can't for the life of me see why discussions like this one keep cropping up again and again. Yes, the series has moved on rather than squatting stubbornly on its initial success model until every last dollar and ounce of fun had been leaked out. Note also that Resident Evil 4 in all of its cross-platform incarnations has sold more copies than any other Resident Evil game, including RE2. Look here to see for yourself: http://www.thegamergene.com/industry/capcom-release-lifetime-sales-figures/
Having the intelligence and will to try and make something even greater on the heels of a smash success, rather than regurgitating what has worked before again and again until it will never work again, doesn't seem like the sort of thing we should be condemning by asking questions like "Wouldn't it be great if nothing ever had to change?"