[twoodfin]

I don't think you're reading Wolfowitz's quote properly. He's saying that the U.S. has leverage over North Korea because their economy is in such a poor state, leverage it didn't have over Iraq because of their oil reserves.

If you're claiming the U.S. would be likely to invade North Korea if they had significant oil reserves, that's wrong. As Wolfowitz says in the context around your quote:

The concern about implosion is not primarily at all a matter of the weapons that North Korea has, but a fear particularly by South Korea and also to some extent China of what the larger implications are for them of having 20 million people on their borders in a state of potential collapse and anarchy.

...

In the case of North Korea, the country is teetering on the edge of economic collapse and that I believe is a major point of leverage whereas the military picture with North Korea is very different from that with Iraq. The problems in both cases have some similarities but the solutions have got to be tailored to the circumstances which are very different.

Hard to draw from this that the "only" reason invading Iraq was more important was oil. The lack of economic leverage made a military option relatively more practical, as did the military and social situation of Iraq vis a vis its neighbors.