Seriously, at some point we're going to hit a wall where the finer detail is pointless because it's more detail than can be seen with the human eye. I suspect we're nearing there as it is. Sure there are plenty of times even on HDTV where details are still blurry or muddy but sooner or later we'll reach digitally the limits of what was captured originally on film. Then, say, we upgrade to these super-HD cameras and then we'll reach the limits of even what the human eye can see without aid.
Well this new Sony set is much higher resolution, but it is also 4 times the size that most people have now, which I imagine is the point. Not to make small TVs in excruciatingly fine detail, but to make TVs bigger.
I think those bemoaning the lack of content are missing the point as well. The standards for HDTV were put in place long before any HD sets were realistically available to the public, they started testing in the 70s, and that is what is happening here. They are betting on the future rather than just assuming things will stay the same, which is kind of what companies like Sony are all about.
This TV is coming out now "because they can", because it is good for their brand to do it. They are not trying to sell it to Joe Bloggs, they just want Joe Bloggs to see that they can and will develop this stuff.