The cinemas are dying because the percentage of people in modern society who can genuinely allow themselves to "submerge" in cinematic experience at a price of 2-3 hours of their life and a cost of 5 movies from Tesco shelf is simply a dying breed.
We are too busy, we have too little time.
While I agree that people have many ways of watching films these days and have very busy lives, hell I work in the industry and don't even go to the cinema as much as I should... but what goes totally against this is that numbers and profits for Cinema box office sales are the highest they have ever been. It's not undergoing anything of a downturn.
What I'm trying to point at is the fact that most of us still have mums, aunts and uncles that didn't even move to full HD TV sets from their DVD home cinemas, and they don't care if batmans face show all the zits and chicken pox craters, they don't care if buildings in spiderman have perfectly rendered CGI edges and they don't care if they can see every hair on blue legs of some creature from avatar. In fact they would probably appreciate more if their Eastenders or Corry were broadcasted in SD at higher bitrate, so picture wouldn't pixelate as much on their argos freeview box hooked up via SCART to their 100Hz CRT (which "used to cost two months wages back in a day, you know and it has brilliant picture"). And it's not only them - most of us with early plasmas and flat screens, watching 99% of all broadcasts in SD, too low bitrate for fast movement and standards converted budget HD channels - 3D is something we never asked for, never wanted and was the least of our problems. For me, it would be - if all my terrestrial and satellite channels were already in HD, in proper quality, without conversion artefacts, with surround sound, at that stage, MAYBE, I would be interested in adding extra dimension to my experience. Otherwise, I bet most of us, just couldn't care less.
People may not care, especially as you point out older people, they aren't rushing out to buy the latest tech compared to the younger generation.
However that's not how it works.
Technology doesn't last forever... I got ten years out of a Sony Home Cinema Amp which was pretty impressive to be fair. What I'm saying is that people have to replace their technology in many cases because they have to, rather than it simply being a case of wanting the latest thing.
If you buy a new TV now, good luck finding one that isn't HD. It's that market saturation that eventually makes it become the standard.
3D has a long way to go because there are too many competing formats at the moment and more importantly, the future will really be without the use of glasses. In part it's a format war, but at the sometime it's not, there won't be an eventual looser.
On another note regarding 3D glasses that I've seen people mention. There are different technologies being used, similar to 3D home televisions. If the Cinema is using a polarising system like RealD, then you can certainly reuse glasses. Cinemas using systems like XpandD require their own active shutter glasses which you can't bring your own.
I actually think a lot of the eye and headache issues people have come more from the active shutter systems. If you've not seen it, they usually work by receiving a signal from a transmitter in the cinema. When they are actually active, the shutter is flickering extremely fast right in front of your eyes, but you wouldn't know that unless you've seen it with the glasses running while off your head.
There is also the fact that battery powered glasses run down which can cause inconsistencies. On the last film I worked on, when the batteries will low on the XpanD system, it was even reversing the eyes!
There has been a big push by some of the TV manufacturers to club together to start using polarising technology, which is a bit more expensive but you can use the same polarising glasses you get in the cinema at home.