Look at what a long term (10+ yr) return is on a good mutual fund....that is what you should be making on the money that you chose to invest in a truck rather than in that mutual fund.
From a carrier's standpoint:....if an O/O does not factor in the revenue their BUSINESS needs to make (above and beyond the driver pay) then that carrier is getting free money....millions of dollars of free money because the O/O's are financing the carrier's capital equipment needs (ie trucks) FOR FREE!
You have to look at this as a business that needs to be able to stand on its own feet.