Generally what you do is that you make a target presentation/demo/showpiece that displays the level of quality you're aiming for.
They spend time on polishing up a tech demo- not just for trade show marketing purposes, but also to internalize as a team that this is the level of quality they are going for.
It's quite motivating and encouraging.
Normally, a game is not coming together until near the end. This can leave many people who work on the project for years, somewhat clueless and give them a sense of having no clear vision.
The more correct question would be; Can the full game they are making, reach the visual fidelity by this demo? To which the answer is probably not completely, but one would assume they'll try to get somewhat close.
As more gameplay systems, objects, enemies and so on enter the game, more hits are made on performance, and uncomfortable darlings will need to be killed. It's always like this. That tiny bit of post-processing that looks ohh so nice might very well be sacrificed because it just isn't worth the 10 fps hit when you're playing it moment to moment.
Which is to say, that it is very nice when developers give players the option to choose between lower framerates with more eye candy, or more smooth gameplay with some of the fancier bells and whistles disabled. We can hope the PC version will have a Ultra/High end mode that can take it to this level.