Well lets explore that and put a little thought into what you're asking? What would adding slow movement while aiming gain you in terms of gameplay in Resident Evil 5? Ignoring the issues with the bus being too good of a hiding spot, in the opening area of the demo you are utterly SURROUNDED and chased once you hit the exterior of the house you start in. It's an open environment with multiple points of entry where enemies can get at you as well as the added verticality of the environment (i.e. you can get to higher ground). Not to mention the enemies can climb and move about the environment as well as you can! You, as the player, are forced to keep mobile and pick and choose the moments when you can raise your weapon and take out enemies that are nearing your position. Once the enemies begin to flank you again you will once again need to flee, reset your position, and take out anything you can before getting hurt. That's is a game designed around stopping and shooting.
The pacing of Resident Evil 5 is so very different than Dead Space that I find the comparisons almost laughable outside the games having similiar camera angles. In Dead Space you are, for the most part , dealing with enemies in straight/narrow corridors or smaller "controlled" rooms. Enemies that don't navigate the environment in a really meaningful fashion. In Dead Space, the ability to move back slowly is a viable gameplay option as you deal with enemies that, for the most part run straight at you and do very little to flank your position. That's not a slight towards the game - it's just how it's designed and it does it what it does very well.
Adding slow movement while aiming in Resident Evil would, from my viewpoint, force the developers to make some rather big changes to how the enemy AI interacts with the player and the environment to make that movement a viable gameplay option that's actually meaningful. Not something that's just added to shut the mouths of the people that can't wrap thier heads around the decision Capcom has made with thier game. That's my personal opinion.