The main problem with the static level check comes from the torque converter. Unlike an engine, which circulates oil and allows and/or encourages the oil to drain back to the pan quite quickly, an automatic trans mission has a large reservoir in the form of a torque converter. The fluid is pumped up and into the torque converter whenever the engine is running, through passages in the middle of the torque converter. In a perfect world, when the engine is shutdown the fluid would all stay in the converter, however, much like the "frictionless pulley" mentioned in a post above, we don't live in a perfect world.

So fluid drains out.

Slowly.

Or quickly.

Depends on the car.

And not just the make and model of the car, but on the individual car. Wear and manufacturing tolerances, temperatures, just about any variable. And that means that some cars' torque converters drain back in about an half an hour and some cars take weeks.

That pretty much means that a static reading is not practical, if even possible.

Besides, when it comes down to it, the static reading isn't what we're concerned with. What we really care about is the fluid level during operation, which the current method, while a bit time consuming, does a fairly good job of checking.

MV