I'm pretty sure it was a design decision (and one I applaud, at that), because it ties in to the series roots as well as helps to induce suspense (or frustration, depending on your viewpoint, I guess). It's a hell of a lot suspenseful to deal with crazy plagas and shit when you have to choose your vantage point and then stop and pop while the crowd is coming for you. It puts an emphasis on thinking about survival instead of just run and gun mindless action. Where do you stash Ashley if she's with you, where's the most tactical vantage point for defending against the horde with whatever ammo you have left, etc.
RE4 wouldn't be RE4 without the controls. Do they take somet getting used to? Yes. Would I like to change a couple button mappings? Yes (namely R1 and L1, since I'm so used to pulling the left side to pop into aiming mode from the modern shooters). Would I change the tank-rooted controls of this game? Not on your life.