More specifically it comes down to earning your way into divisions. This helps out newbies on the field too, as it keeps the elites off it.
The most exciting aspect of Halo: Reach is likely the new Arena system designed to keep those so called elite on their toes. Basically they fight in month-long seasons to prove just how dedicated they are to the cause - with ratings and skill divisions.
It’s not down to pure kills though as Bungie know assists can be just as valuable in a match, with other factors also influencing where a ‘hardcore’ will end up. The division names are Onyx, Gold, Silver, Bronze, and Steel.
Players need to acquire ‘Daily Rankings’, which means they need to complete a certain number of matches a day in order to get an average. The extra goodness from all this is that super elite players will be kept away from the more casual - a win-win really.
Shacknews has more on what Bungie has in mind for Halo: Reach. Arenas proved popular for the hardcore in World of Warcraft so it should translate well here, right?