I have an odd question that as far and wide i have looked i can't get an answer so maybe today is my day. Why do they make different sets why not just make them all one. I dont know can you not play different sets like infinity and dc icons. i don't know if someone could help me out that would be awsome. I ask this becasuse i use infinity and my girlfriend uses dc icons.

Well, in a sense they are "all one set" because they all use the same set of rules. Since they all use the same rules then they are all interchangeable. DC Icons is the latest set of rules and they override anything printed in the Infinity Challenge rules. The Infinity Challenge rules are out of date and no longer used (however the figures are perfectly fine to use).

Another reason they make different sets: Heroclix has been out for several years now. The game has evolved since then; powers and team abilities, feat cards, BFC's (battlefield conditions), giant figures, and more have all been added since then. The rules have changed quite a bit too, like Stormfang said. Now since Heroclix is a Single Universe game, you can play them all together any way you would like....the only exception to this is in Contructed tournaments where retired sets are not allowed.