One point that was made over on Alex's Planetary Sciences discussion group (forget who by though) is that although the ridge is currently on the equator of Iapetus, it doesn't have to have formed there.

It may have been created elsewhere on the planet, forming a mass imbalance compared to a perfect spheroid. Then tidal forces and spin axis instability could have caused the whole moon to tilt until the bulge lay along its equator. This is a similar process to the Tharsis bulge lying on Mars' equator - it doesn't have to have formed there. Even though Iapetus is tidally locked to its primary, this process still works because Iapetus is still rotating (once per orbit).

An interesting paper recently posted on JGR Planets in Press discusses evidence for a former spin axis of Mars, evidenced by giant impacts on the palaeo equator.

For those with the time and inclination to plough through full scientific papers, PIP is an open access site where one can browse a selection of recent planetary papers. There are several mars papers there right now. the content is always changing, with older papers expiring as they are formally published.