How come out of interests?It's nothing to do with his narcissistic tendencies (which I don't dispute) but more likely to do with Equity rules; if someone else had already registered the name 'David Williams', then he'd have to choose a different stage name.
There’s two famous Brian Coxes, two famous Michelle Williams, two famous Chris Evanses etc. Find it a bit odd that Equity can’t accept that two people may just have the same names. It happens.