Great tech doesn't a good game make. COD has the money to get the best there is because they are a cross platform seller. Halo, being X-Box exclusive, sometimes has to cut corners to be sure of a profit. This is an example of a corner cut. No one can be sure that Halo 4 is going to be a best seller since it's the first of a new trilogy, so the decision was made to cut some corners to make things as profitable as possible. This, of course, is only one reason of many for 343i using Reach's engine in Halo 4, but I don't have the energy to make an 8000 word essay right now. lol
Also, on a side-note, COD has copied many things from Halo in the past. Don't believe me? Play any game they released prior to Halo's release, then play the newer games. See how many you can spot. lol