You know how trailers of work-in-progress games sometimes look better than the finished game? That's largely because they're unfinished, unoptimised, and running on production hardware, so no one's yet ordered folks to beat the beautiful out of them so they'll actually run. It's misleading, and while it does build anticipation it also leads to crushing disappointment. Ubisoft have felt that wave of disappointment crash over their faces, which is why they say they're stopping doing that.
Open-world crime uncle simulator Watch Dogs looked jolly pretty at its debut during E3 2012, but trailers became less attractive - as Nathan noted - leading up to its launch in 2014. it looked a fair bit less attractive than its showing at E3 2012. Folks fiddled with files to restore some of the old look, but it was a bit wonky and not quite the same. (I maintain that Watch Dogs in its original super-cinematic state would've been near-unplayable with all that blur and murk, but hooo it sure was a lot prettier.)
Anyway, the point is: Guillemot says they're now reluctant to repeat that.
"With E3 2015 we said, OK, let's make sure the games are playable, that they're running on the target machines. When we show something, we ask the team, make sure it's playable, make sure gamers can immediately see exactly what it is. That's what we learned from the Watch Dogs experience - if it can't be played on the target machine, it can be a risk."
So they say. I wonder how long they'll stick with this policy - and how they'll deal with perhaps needing to tweak games before launch as unexpected problems crop up.
I also wonder if this means they'll ease up on 'bullshots' too, those staged and tweaked screenshots which look far prettier and more dramatic than the game ever well. They've certainly been guilty of that too, along with half the games industry.