In all fairness, there is also some of it used for Box Office and On Demand. 15 movies * 1.5 hours (Box Office) = 22.5 hours; plus whatever is on the catchup service. I agree, the compression is probably rubbish, but most of these things come with 5.1 soundtracks and it is substantially more than just 50 hours.
Based on this comparison, there is absolutely no reason I can think of to buy the new decoder. Just a question - if the usb and ethernet ports get enabled, what are you going to use it for? Charging your iPhone? My PS3 can browse the 'net, but the interface is crap, therefore I cannot imagine wanting/needing internet connectivity on a decoder.