They talk about a 4 year timespan. The Oculus Kickstarter was in 2012. DK1 was released in 2013, DK2 in 2014, and the final Rift in 2016. The Rift-S is rumored to be released in 2019. None of those have had quite the leaps 3d did back in the late 90s.
For contrast, id went from Doom to Quake III Arena in six years (Dec 1993 -> Dec 1999). Thanks to the rapid pace of graphics card improvement and the engineers writing the software engines to keep up with it (Carmack, Sweeney, etc).
