This may be a case of waning interest in many areas coupled with the lackluster economy. Gone are the days when the average "publisher" could uproot his whole family and traipse to New York for a delightful 8 day festival of spiritual gorging. Just think what such a thing would cost today. Again, partly because of the economy in general but also largely because of the Society's discouragement of higher education and the careers that go with that, most of the "brothers" simply couldn't afford something like that. Oh, some would wreck themselves financially to try to make it, but I doubt nearly enough could actually pull it off to make it worthwhile.
I was in NYC as a child for both the 1958 and 1963 for the International Conventions. They were indeed 8 long, long days. Everyone, including the most ardent adults, was exhausted both mentally and physically at the end of each day. I doubt anyone retained very much from the ceaseless pounding of spiritual drivel into their skulls.
Anyway, reducing the conventions from 3 back to 2 days may be a back-door way to try to increase attendance. Of course, I haven't been to a JW meeting of any kind in about 10 years and will never go to one again, but I can see why they may want to try this out.