I would be interested in knowing how you calculated your numbers. I did some digging and found an old (10 years ago) report from the Univ of Illinois on the operating costs of taxis in Chicago. In round numbers, the typical taxi driver brought in just under 60K/year in revenue and had 42K/year in operating costs. Assuming there hasn't been a major upset since then, this is a very long ways from 10x.
I'm figuring that a typical taxi driver might make $30/hour and in that hour drive about 20 miles. At 30 mpg and $3.00/gallon gasoline that's about $2 for gas. Figure that a typical car costs $20K and lasts for 200,000 miles, so 20 miles = 1/10,000 of the car = ~$2 in depreciation. Maybe another $1/hour in maintenance - that'd imply about $2K/year, which seems high, but this is higher mileage than a family car anyway. Total about $5/hour, which would be around 1/6 labor costs; not quite 10x, but around that ballpark.
Switch to electric vehicles (which are suddenly feasible with the car-service, never-have-to-park model!) and centralize maintenance across a whole fleet of cars and you can shave a bunch off gas & maintenance, though your depreciation would probably go up unless battery packs became dirt cheap.
