Like edczxcvbnm said, its essentially a moderately informed guess. I also agree that you shouldn't put your money on things coming out in those time frames. I have a sliding scale of personal expectations.

TBA (year) - don't hold your breath
TBA (quarter) - be cautiously hopeful
date more than 6 months away - hopeful but ready for disappointment
date under 3 months away - pretty sure thing


Oh yeah... one other category

Blizzard or Valve game - sometime after your unborn child gives birth to your first grandchild