The graph is a list of outliers rather than a realistic representation of game dev schedules. While there are plenty of wildcards like team size and experience, I'd describe things more like:
- 2 years start-to-finish is normal for AAA titles (the Call of Duty games for example)
if the studio is well oiled, firing on all cylinders, and hits the ground running. (Alpha ~15 months, Beta ~18 months.)
- 18 months start-to-finish is a rush for AAA but normal for a cheaper game such as a movie tie-in.
- 12 months is an ugly quick production for even a cheaper console game, unless making a sequel or DLC that reuses the same engine and many assets. If working without existing assets then its Metacritic score is probably going to be ~65
- Less than 12 months is moving more into phones/handhelds/freemium rather than console productions.
- 3 years is for an AAA title that involves a bit more unknown territory, or the project got into trouble, or the product is a platform flagship, or a land-grab into a market dominated by an established competitor, etc.
- 4 years and more is mostly MMOs, a few huge AAA productions, backburner projects, and AAA clustertrucks that were able to go beyond schedule for some reason or changed direction mid-production or some other unusual situation (eg HL2 and TF2 were funded by GabeN until they were done, whereas a publisher generally won't do that)
- Honorable mention to Duke Nukem...
(Elite is an MMO built on unknown territory and ambitious in scope. To my thinking, even though it's going to require a long time they're cranking it out quite quickly.)