Random Observation

[amyxaphania]

Joss Whedon must have liked the name William and its derivatives...

William the Bloody

Liam

Willy the Snitch

Billy Fordham

Billy (the kid from Nightmares)

Willow (a stretch, but if you take the 'Will' part...)

Did I miss any?

Comments

[debris4spike]

Seems as if you have uncovered some secret!

:-)

[cordykitten]

I've checked Wikipedia and some others, can't find other names there.
Indeed, JW seems to love William.

[henriettaholden]

Angel had an episode called Billy

[aerintine]

It was always curious to me that Angel and Spike had the same name as humans. Never thought about all the other derivatives - interesting thinkies.

[ladyredraven]

"Keep your head up, Billy buddy." - Dr. Horrible

It's not just in Buffyverse, though that's probably more of what you were going for. :) I never would have noticed this.