Ah, I didn't realize you were talking about this, I thought you were referring to format (3:2).
of course, the main reason for the slow transition to formats like the micro four thirds is that the current electronic viewfinders (lcd screen) are still way worse than optical pentaprism viewfinder. Even so, most modern DSLR have live view and can capture movies (in a couple of months I hope to own one of these too).

(nitpicking: it's not the prism, but the mirror that jumps with the shutter)