Isopropyl alcohol is a fast drying solvent. It may or may not dissolve residual contaminants from polish, wax, sealants, environmental contaminants, etc.
If the polish is dissolved into the IPA on the surface of the paint and is wiped up, where do you think the dried polish is when the IPA in the towel dries? For example, think about the polish "cement" left over on occasion with M105 if we don't wipe it clean before it dries on the paint. If you use IPA or MS, it's in the towel.
We already know that an IPA wipedown can leave streaks which are probably contaminants (polish, wax, sealants, etc.) that were solubilized but were left behind dissolved in residual IPA when wiping with the MF towel. I would guess that 100% mineral spirits would leave residuals behind as well, except MS may 1)evaporate more slowly so the polish may stay solubilized in the towel after removal and not get left behind on the paint, 2) the MS may remain on the paint surface in solution phase so we can't see the dried residual on the paint, or 3) the MS has residual oils that mask the contaminants. I vote for number 1 or 2.
MS may also keep the polish from drying in the towel, so the softened polish may not scratch the paint as easily as the contaminated towel used with IPA which may allow the polish to come out of solution (like the hard cement like stuff we occasionally see while polishing). MS and IPA are not equal solvents with the same materials (they fall out of solution at different rates and concentrations).
While I'm not an organic chemist and have not spent anytime in petroleum distillation, I'm not so sure that mineral spirits have a lot of oils in it, unless they are specifically added for some reason. It may (probably does) have a number of hydrocarbons that co-distill at the same temperature and it may or may not be run through a series of filters to remove specific contaminants. The oily feeling that Mark mentioned could be oils or how the solvent solubilizes/interacts with our skin.
As a side note, mineral spirits are sold in three types (I-III) and we use type II which are known as white spirits (I googled it). Mineral spirits were the dry cleaning solvents used up through the 1950's, so it shouldn't leave too many oils on fabric.
Since MS doesn't dissolve paint and seems to be a good solvent for polishes, waxes and sealants, I would guess that it is a base solvent in many care car products such as bug and tar remover and some pre-wax paint cleaners. Four Star paint cleaner smells like MS to me.
Mark, fast drying mineral spirits may be a more pure distilled or non-adulterated form that happens to evaporate faster but it could be just "marketing." Don't buy the white, environmentally-safer mineral spirits that I bought for a cabinet restaining project that I started this summer. It's CR@P.
If you wanted the ultimate paint cleaner, I would guess that an automotive paint shop specific paint cleaner would offer the broadest "cleaning" capabilities. I just don't think we need to think that hard.
This is a great post, full of information, but... why is it that the IPA process seems to be hit or miss? The way you describe this it should happen to everyone, when in fact it doesn't. If I have wiped a panel with one towel and had slight marring, change towels and use the same chemical with no marring, how is this possible if the IPA is crystallizing the polish and embedding itself into the towel?