Strictly speaking, the application for GC and N-400 have nonidentical questions about "other names". Let's compare:
Application for immigrant visa and alien registration: "Other names used or by which known."
N-400: "If you have used other names provide them below."
Hope you see the difference: OTHER NAMES BY WHICH KNOWN. This is much more broader notion than "other names used." For instance, you may be known to other people by different names merely because they cannot pronounce your true name correctly. Another possible case is when the grammar of some foreign language requires a transliteration different from the English spelling. N-400 asks only about names you (and only you!) ever actually used to identify yourself. So, why should one care about all nicknames invented for him by others and probably without his knowledge and consent?
My personal exerience: when I applied for GC, I mentioned French transliteration of my name because I knew that the French spell it differently and I knew how. After all, this is their inalienable right. Theoretically, I was not obliged to mention that French version of my name, because it was a complete fluke that I happened to learn some French once in my undergraduate years, so I was able to read. Indeed, there are as many possible transliterations of the same name as there are many languages. However I am not obliged to know all foreign languages and monitor how those guys modify my name. So when I applied for citizenship, I did not mention the French transliteration, especially as I never used it officially (and inofficially) myself.