The lithium soap is just one type of thickening agent - it has no real effect on the lubricating qualities of the grease as such. The oil contained in the grease is the important part (plus any additives like molybdemun disulphide etc.) All the tickener does is hold the oil in contact with the bearing surfaces between services. Some thickeners are better at resisting water than others, some better at dealing with high temperatures etc. Lithium is just one of many kinds of thickener that fall into the "general" use category, and its relatively cheap. Lithium is the basic all-purpose grease.

If you want to read up on grease, this site explains it pretty well...

http://www.machinerylubrication.com/Read/1352/grease-basics

__________________