[ausev] 2 motors - serial vs. parallel

[evehicle4me at hischopsticks.org]

I was told on another forum that if you had two motors in the same car  
- one on the right and one on the left - and you hooked them up in  
serial you would not need a differential.  The reason stated was that  
the force of the wheel on the ground itself would cause one wheel to  
slow down and the other to speed up.  Does this make sense?   Is it  
right?  has anyone ever tested it?