It's a pretty unique first name, and I feel like people (online, and IRL) refer to him by either first or last name 50% of the time.
Sergey Brin also comes to mind. Unique name, people don't really say "Brin". Just Sergey, given the correct context.
I don't think this is a case of people thinking they're "best buds with the man," like when people rarely referred to Jobs as "Steve."