The retina displays on the iPhone and iPad have been very popular, with their high resolution and amazing sharpness and clarity. That's the good news. The bad news, according to All Things D, is that these higher-resolution displays are resulting in ever larger apps that take up more memory. This is true even if you don't have a device with a retina display, such as my iPad 2. That's because developers make a single app for iPads that automatically displays correctly depending on which iPad it's running on.