You're missing the point, I think. "will.i.am" is a stage name, not an anonymous handle. Whatever you think of the validity of the rule, surely you agree that its spirit is to make sure you can always clearly associate the account with the real person it belongs to. Surely you agree that the existing name achieves that better than "William James Adams, Jr.", right?
The point was more subtle than that. It's not merely "most people" in this case, it's a public account for a celebrity. The overwhelming majority of people, and essentially all of the target market, have no earthly idea what his real name is and don't care.
Regardless of what you think about whether this is a good or bad rule (and I tend to agree it's a bad one), no one is served under any interpretation of the rule by disallowing celebrities from posting under their stage names.
Basically, if it's an exception to the rule, then it's a sane and well-justified one. If it's a subtle edge case, then so be it. I think it makes very bad evidence of hypocrisy on Google's part.
