Since point two has already been debunked enough, (though there's plenty of room for more), I would not that Tian'anmen is "correct in untone official pinyin" that of course is used by almost no one, inside or outside of china.
As for your third point, since you can read chines you know that there is extensive information on the page talking about other commonly used names, many of which include the Tiananmen phrase. In fact, the first section of the chinese article goes into a fair bit of detail about that. Furthermore, seeing as wikipedia is hardly democratic, or used under "free conditions in China", I see no reason to use it as the baseline for determining what is common, or the common usage of certain terms, especially a term that connotes an event that the majority (or a substantial percentage) of chinese people under say, age 30, have never heard of.
As for the "needlessly sarcastic", when did the internet become a place where sarcasm eternally brought about the wrath of other commenters? Is the problem the "needless" sarcasm, as opposed to the sarcasm in general? Doesn't personality mean anything? And if it's the "needless" part, let's be honest, is hackernews really "needed" at all?