Another year or so?
"Clearly, this tablet is designed to show off Windows 8 at its best, but it raises the question of how well the new OS will run with less powerful systems."
ARM Socs are getting more and more powerful for the same power consumption and even Intel appears (although a little late in the day) to have woken up.
"Intel promises '20X' power reduction with 'Haswell' chips" (http://www.theregister.co.uk/2011/09/13/haswell_at_adc_2011/)
The time when hardware capable of running a full song with choruses os without slaughtering the battery is rapidly approaching. I honestly do not believe that is going to be a major issue. Things are developing so fast that in a couple of years time at the very latest the specs of that Sammy that MS have given the attendees at Build will be regarded as *very* ordinary and as you point out are fully capable of running a full fat os without sweating.