In my opinion Photoshop is absolutely inappropriate tool in this new era. It was never really meant to design user interfaces. Designers should finally stop thinking in terms of pixels as they don't really make any sense if your application will be shown on screens with more than one kind of pixel density.

There should be no problems with using vector graphics on high resolution screens and it will look much better on lower resolution screens than downscaled image. Not only will vector graphics make support of various screen densities easier it may also (significantly) decrease size of assets. Currently on iOS devices developers bundle two images for same purpose (1x and 2x). It could have been one vector image instead.

Please stop using tools which were made to edit images and start using ones which are made to design interfaces.