I don't think that was the point of the exit interview article. My understanding is it was mostly that nothing you say will make any difference to the company, in all probability - so there is no need to go into the interview looking out for anyone but yourself.

And definately do not go in to air your grievances.

But I generally agree with the mercenary approach, my personal ethos when working for a company is - take as much money from them as possible and provide my best estimate of (money+some reasonable extra) back in value.

The reasonable extra is an investment of time and effort with the goal of paying out as more money later.