The question is not is why does Siegler care. He can reasonably expect to care: it's his photo attached to his personal profile and his photo is part of how he chooses to portray himself online. Siegler now knows that he cannot be himself on Google+, and now thousands of others know that they cannot be themselves on Google+ either.
The question is: why does Google care so much that about the minutae of how individuals choose to portray themselves while they face much greater problems related to the success or otherwise of their new social network?
Putting aside the spam problems that render Google+ at best noisy and at worse useless, if Google is so intolerant that it silently censors a hand gesture considered impolite in where their HQ is based, how else will they behave? Will they censor every gesture that might be considered offensive somewhere in the world (there are many)? Or will they remain purely focused on the North American hand gestures, and, by extension, North American culture and the limited audience that it brings?