Actually, as far as my knowledge of the matter goes, films for cinematic projection are delivered to cinemas on huge external HDDs because they are uncompressed HD. A losslessly stored digital film at 1080p will have somewhere around 300GB, which by today's standards is not that much, a 300GB HDD is considerably cheaper than 2hrs worth of 35mm stock and the transfer of the digital data to the HDD is virtually free, so there is no reason for the cinemas to project from compressed sources, that wouldn't make any kind of practical sense.

But I agree that the picture quality depends greatly on the quality of thedigital projector in question and also on the size of the screen. Where film simply looks less detailed on bigger screen, digital will reveal the atrocious projection grid, which really annoys me...