I do know what web developers are interested in, however. They need CSS pixels. That is, the “pixels” that are used in CSS declarations such as
These pixels have nothing to do with the actual pixel density of the device, or even with the rumoured upcoming intermediate layer. They’re essentially an abstract construct created specifically for us web developers.
Also, DPI and websites:
Safari actually supports PDF as an image format (the hands of the clock Dashboard widget are an example of this). However other browsers do not support this format. The agreed-upon standard for scalable graphics on the Web is SVG.