You Learn Something New Every Day.

[AgentZero]

I've yet to see a game that didn't list both, and I look at a good few. Personally though, I always just look at the Recommended spec and take that as the minumum, since I've always figured that the way minimum and recommended specs get onto a box goes something like:
Devs pass minimum specs to Marketing.
Marketing cuts the specs by 25-50% and puts those down for minimum spec.
Devs find out and raise hell.
Marketing 'compromises' by adding the devs minimum spec in as the 'recommended spec.

Either way, I usually just read the review in something like PC Gamer where they tell you what spec they recommend, so you know what you need in order to run it and have it look like it does on the back of the box.