I think it's because a voltage output would be sensitive to wire resistance, voltage drop, and steady supply. A TPS and MAP sensor really aren't THAT important, they just need to be pretty close. A MAF on the other hand has to measure correct airflow to control the fuel precisely.
Here's the twist, why couldn't the MAF have a 0-5v output with a dedicated regulated power supply like the TPS and MAP?
Or did GM do it because it's rare that they ever get to use the built in timers with one of the gazzilion digital inputs?
Maybe all of the above.
Anybody else have any ideas without cheating and asking GM .

 

To further the question, why does that "Other" manfacturer (Ford) just use a 0-5 volt signal for the MAF? Must mean that the digital is not a requirement of the MAF, but just the way GM cared to implement it? Interesting question indeed...

 

As you probably already know, the tps and MAP need the constant voltage since theyre position sensors. In the tps, there is basically a resister thats hooked between ground and constant +5 volts and a contact along the resister that moves with the throttle. The output is hooked to the contact and as it moves along the resister it provides a linear 0-5 volt output. Without a dedicated, regulated power supply, the voltage would vary and screw up the readings.

The maf has a bunch of circuitry junk in it so it can generate whatever outputs wanted so battery voltage is probably fine. As for why frequency or voltage, I donno...

 

Greater dynamic range and less susceptible to noise.

RBob.

 

Noise, that was what I was trying to say, lol.
The dynamic range is interesting. I did some math and the range for a 0-5v with an ~4v range; 8-bit ~ 0.015625v and 16-bit ~ 0.000061v . What are the timers built into the processor? Isn't there a 160, an 100, and 80hz in the c3's? I could find out but I'm too lazy right now.
I have a feeling that GM uses the frequency and 16-bit to decrease the latency fuel correction effects. Example; with an 8-bit it might take ___ms before the ecm knows that the air flow is decreasing while it would take less time for a 16-bit MAF to react.
I know this is pretty random but I haven't learned anything new in the past few days.....