I have been riding motorcycles with chains for the past 20 years. I use WD40 to clean the chain because it works great! Afterthat, I lube with a non-flinging wax. I have the same on my MTB bicycle chain as well.

All my motorcycle chains have lasted 25k+ miles, which is beyond their normal service life. I don't see any reason why WD40 should not be used to clean bicycle chains.

BTW, cleaning a chain and lubing it are two different things.