It seems like almost every day a new rumor regarding Apple surfaces. The latest rumor says that Apple will debut a refreshed MacBook Air at this year's WWDC taking place next month. A refreshed MacBook Air is expected to make use of Intel's new, low-power Haswell CPU's and possibly feature a Retina display.
One of the main reasons this rumor has popped up is that availability of the current 13-inch Air with a 1.8GHz processor and 256GB SSD is out of stock at many large retailers across the web. Amazon, B&H, MacConnection, and MacMall are all out of stock, while J&R is only offering the system in-store.
Supply constraints are often an early indicator that Apple is planning on releasing a refreshed model. In anticipation for the new model, production of the old model ramps down to clear existing inventory. WWDC takes place shortly after Intel debuts its new Haswell processors and would be an excellent time for the unveiling of a refreshed Air.