It's not really about limo v not limo, it's really the other way around: you can charge either for time only or for time + distance, if you charge for time + distance you need a tamper-proof meter.

Time-based is mostly used by limousine services and time+distance for "regular" taxis for obvious reasons (a limo tends to be rented for a long time but not to move far, the opposite is true of regular taxis) but nothing prevents a limo service from charging for time+distance (besides looking cheap) and nothing prevents "regular" cabs from charging for time only.