Firstly they do give offers to most aslong as you have an A in AS maths i think you should expect to get an offer. I've done STEP but not AEA so i can't compare the difficulty, although people have said AEA is easier. I don't think STEP takes away weakers students, i personally found STEP alot nicer than Further Maths for various reasons, where as for some people it's the other way around, so who is weaker (both cases could be argued equally) ? Because Warwick give so many offers the chances of missing your offer and getting in a extremley small (taking into account external factors). I've read about 3/4 people who miss their offer will be allowed in. So if you don't meet AAB/2 or AAAA unless you have something extra like a very good STEP grade or a valid reason it's very likley your not going to be allowed in. As for why it's Fifth, according to the criterion they've used that's where it should be, the validity of the criterion are questionable however.