Is IBIS better than OIS?

The subject seems to be a hot topic right now, especially with the K1 release upon us and quite a few ML sporting IBIS now. In a recent thread I can't remember the specific name of, IBIS was touted as superior by many. I admit, correcting for "roll" is something that OIS can't really do, which is a big advantage for IBIS, and people were fairly quick to point this out.

So rather than just focus on opinions of which is better, I had a spin off question. Why do MFG seem to always use OIS when they create fixed lens cameras? From the RX1rII to the LX100 to the RX10, they all use OIS. So this naturally seems a bit counter intuitive, if IBIS is superior, why do none have it?

I had a few potential theories, from size restraints to cost, but these don't seem to be the answer, not EVERY time. Cameras like the FZ1000 are downright huge for a 1" non-mirrored fixed lens. The RX1r/II are very expensive already, was IBIS cost just too much to add in?

Im just curious as to why these brands are insistent on IBIS (with the exception of Panasonic as they do both) in their ILC, yet they won't stray from OIS in fixed lens bodies. Any ideas? No flame war please, Im more interested in amicably finding the reasons as that may give new insight on the IBIS vs OIS debate.