Keep in mind that even if you're maxing the in-game settings, you aren't maxing out the image quality fully. You can still go beyond that with supersampling (essentially rendering at a higher resolution, then downscaling to your monitor's resolution in order to prevent aliasing). Standard anti-aliasing tries to detect edges in order to find specific parts of the image to supersample, but it isn't perfect. If you want the best image quality possible, supersampling is the way to go.
The downside though is that it's extremely resource intensive. Even 16x MSAA antialiasing is faster than 2x supersampling. With supersampling, at 2x on 1080p you're rendering at 3840x2160 then scaling down to 1080p - effectively the same as gaming on 4k.
I have two rigs, one with dual r9 270s and another with SLI'd gtx 760s. Each can run dota 2 at 2560x1600 with 2x supersampling at around 40 and 30fps respectively.
The image quality is beautiful, don't get me wrong, but even those cards in an SLI isn't enough to push that amount of pixels.
With quad Titan Z's, you could probably do 4x supersampling - nearing the quality you'd get with source film maker, but in real time.
Personally I find having a higher frame rate in faster paced game is far more important than having a diagonal line be perfectly smooth. In the middle of a game you'd never be concerned with how perfect the image looks.
But going from nearly perfectly smooth lines to perfectly smooth lines should not be a profitable market. Nobody will notice the difference during any real gameplay. You can already do great anti aliasing so why would someone pay $1000+ more for a 10% or less gain.
I think the main purpose it serves for Nvidia is branding. This gets plastered all over the tech news and everyone knows Nvidia makes the fastest GPU. People then associate them with better technology (for better or worse).
Why someone would buy it? There are a lot of people who want the very best. It's the same reason people buy an Aston Martin over a Toyota.
From a more practical perspective though, there's also future proofing. This card will be able to deliver high frame rates for a few generations of games. People who don't want to regularly rebuild their rigs might prefer this card.
The downside though is that it's extremely resource intensive. Even 16x MSAA antialiasing is faster than 2x supersampling. With supersampling, at 2x on 1080p you're rendering at 3840x2160 then scaling down to 1080p - effectively the same as gaming on 4k.
I have two rigs, one with dual r9 270s and another with SLI'd gtx 760s. Each can run dota 2 at 2560x1600 with 2x supersampling at around 40 and 30fps respectively.
The image quality is beautiful, don't get me wrong, but even those cards in an SLI isn't enough to push that amount of pixels.
With quad Titan Z's, you could probably do 4x supersampling - nearing the quality you'd get with source film maker, but in real time.