Citation from the 2003 SL55 AMG owners manual under "what to do if ... the yellow check engine indicator light comes on"

  Have the vehicle checked as soon as possible by an 
  authorized Mercedes-Benz Center.  An on-board diagnostic 
  connector is used by the service station to link the
  vehicle to the shop diagnostics system. It allows the
  accurate identification of system malfunctions through the 
  readout of diagnostic trouble codes. It is located in the
  front left area of the footwell next to the parking brake.

And this is only after checking the fuel cap and ensuring the fuel tank isn't empty.

They don't recommend towing the vehicle. There are surprisingly few conditions mentioned in the manual where a tow to the service center is recommended: brake system failure indicators, and visibly dangerous tire damage/vibrations.

There is however substantial discussion of towing methods and proper towing procedure, mentioning significant risks of damage when done incorrectly. So we see, towing isn't some kind of panacea the manufacturers are eager to suggest - the process may break things like the transmission or body if done incorrectly, especially over long distances.

It's a noteworthy difference in the failure modes of Teslas (and perhaps EVs in general) vs. conventional ICE vehicles.

ICE vehicle drivetrains often fail more gracefully. The first vehicle I purchased, to rebuild before getting a driver's license, had a broken con-rod, yet it still drove noisily with a hole in the side of the engine block.

ICE vehicle manufacturers do not actively disable a vehicle in a CEL-triggering condition. They want nothing to do with potentially pro-actively stranding someone, which could be a life-or-death situation like a snowstorm, just because some sensor is malfunctioning on an otherwise perfectly operable automobile.

Requiring a tow is a self-evident condition. It's been generally left up to the owner to decide if they want to risk potentially costly repairs driving with an indicator light flashing.