I don't ever see them dumping the assemblies. The largest consumer of WT publications are..............JWs. Those assemblies and conventions play a role as promotional events. I think too, like another poster mentioned the social aspect of those large gatherings has a positive effect on the pysche of the average JW. We don't do birthdays, proms, holidays, etc.. The only social extravaganzas JWs are ok to attend is the conventions, assemblies, and the Memorial. JWs buy new dresses, new shoes, new suits and dresses for the kids. JW women desperately try to lose weight starting months in advance of these events. After the convention, people are temporarily on a spiritual high. "This was the best one yet!!" "This old system was beating me down, but this assembly was right on time!!" Granted none of them can give you a logical explanation why they're on a spiritual high, but the feeling is all that matters. The powers that be recognize this and will continue to promote these events. Plus being around a bunch of people that you share a common bond wth does wonders for promotion of sticking with the herd. Even when I was in school, the worldly fellas would allow me to tag along. I felt like I was part of something then. Patriotic people feel the same way waiving their flags and standing next to their fellow Americans. Its the same thing with conventions.
Arrogance on the part of the powers that be plays a role too I believe. I say that because they really make a major stink about skipping the Friday session. They really have a problem with people using their job as a legitimate excuse to miss the opening day of the District Convention. On top of that they want you to be at your seat before the opening song, so you can "enjoy the music that was prepared specifically for you." They really announce it in that fashion, so I take it they really think we're enjoying the music.