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.
They're not a panacea but they are an enormous upgrade from your 1x raster.
I liken this situation a lot to adapting a site to multiple devices with media queries. Does it help? Oh hell yes. Would a unique mobile site be better? Probably, if you had the time and resources to commit to it.
Of course custom raster will look better, but I don't think it's realistic for most teams. If you didn't handcraft the pixels of your favicon you're not a candidate. Vector solves much of the problem and will continue to, even when new densities come out.
You can do <img src="logo.svg"> in IE9 and every other browser. In fact, you can do an inline <svg> image inside of your HTML in all those browsers as well. The <embed> is long gone.
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.