I suppose some things are sort of fixed by not being mobile or not intended for mobile use. A packet of cornflakes maybe?
But somethings are intended for mobile use and are mobile. Mobile phones for example.
So, for the EU I believe that there should be a people's rate that is applicable all over the the EU.
And yes, it should cost the same in Slovakia, Slovenia, Iceland, UK, France, Germany, ... on a very simple basis: we the people seek this mobile functionality at a rate that the people can adopt easily.
(I'll just dream on and along though and will not hold my breath waiting for it to happen)