Oh United. Just when you looked sexy again you turn around and make a grab for our wallets.
Elite status on airlines are generally based on amount flown - whether it's segments or miles. If you fly 30 segments or 25,000 miles in a calendar year, United would grant you Premiere Silver. Double that gets you Premiere Gold, and so forth. Now, United is adding a minimum spend requirement for 2014. To get Premiere Silver, you'd better have spent $2500.
This shouldn't really hurt business travelers, since they tend to pick up more expensive fares than us webfare loving folks, but it does further irk flyers. Even if you're a top tier elite (100,000 miles) you'll have to spend $10,000 to keep your status. So now our miles aren't necessarily the most important thing anymore - it's all about the money.