Don't forget funding agency demands. Just got a new five year project? Of course you need a deliverable after 12-18 months. Nevermind that you haven't had any chance of producing good science in that timeframe (unless you take the PhD comics version of the grant cycle as literal advice)
As an aside, I have seen that grant cycle given to new grad students by a senior researcher as the way things are actually done. And I can't say I actually disagree.
http://www.phdcomics.com/comics/archive.php?comicid=1431