This is FUD. Anyone who owns a car should check their ATF on occasion, especially if shifting does not seem correct or (if equipped) the transmission temperatures heads toward the red.
Basic procedure is always: check ATF level when engine COLD to make sure fluid level is in the COLD range, not below or significantly above. If OK, drive it until normal engine temp is reached, park the vehicle on a flat, level surface and leave the engine running. Finally, pop the hood, extract the transmission dipstick and check that the fluid level is within the indicated HOT range. If significantly over HOT, someone has been overfilling the transmission, or engine coolant is leaking into the tranny via the radiator heat exchanger. Significantly below the HOT range means you've got a leak.
Fluid should be red (DEXRON-III/IV) and not look/smell burnt.
Some transmissions, such as one I have, will look way overfilled when the engine is off. That's why it is important to check it per the manufacturers directions.