I didn’t read all comments but too answer in general: relative size of content is only relevant for future. So drop your Pixels and adapt Ems. You just can’t design app or website that will look great ok 4k tv and 500px mobile phone. Zooming is fine but absurd. Who wish to see squared text on 4k tv? Why most of sites still use px? Well of course those sites were made some time ago or company that made site still didn’t switched on new “technology”. But go take a look at known web designers sites you’ll see just responsiveness.
Take a look at this video. http://channel9.msdn.com/Events/Build/2012/2-116
Designing for screen was under influence of print design, this is now changing in good way. Content is important not a shiny button you wish to shine exactly on all devices as it shines on yours.