Contradictions galore! Since you insist on me spelling it out in layman terms, let me oblige.

A high leakage chip is very inefficient at utilizing power (because of the leaks) so at say 1.20v, a high leakage chip will generally run cooler (than the more efficient, low-leakage chip). The low-leakage chip, because it utilizes power more efficiently also generates more heat because you have to realize that: input power = output heat. What you're describing is a process improvement, not a high leakage chip characteristic. The reason why high lekage chips are suitable for ln2 is simply because they can take more voltage; more voltage=more power=more heat <- needs to be cooled by ln2. Makes sense?