While this is somewhat true, it becomes less relevant over time. As transistor size shrinks, leakage and static power loss becomes more and more of an issue.
AMULET was an attempt to make a commercial async chip and it flopped pretty early, one of the reasons being interfacing with anything else in the entire world kinda requires a clock.
For example , energy micro, one of the leaders in low power microcontrollers use the very old 130nm process, same as those FA18A chips.