A logical though perhaps slightly pessimistic reader asks, "Is the fact that human beings are self-serving, egotistical creatures the only reason that 'I' is always capitalized, while 'you' and 'us' follow the rules that EVERY other pronoun does?"

Disturbing anomaly, isn't it? But take heart. Remember, all the other first-person pronouns--ME, MY, and even the grasping MINE, along with their plural counterparts--go modestly without initials caps. And even "I" has reasons for its perennially superior position. The Harper Dictionary of Contemporary Usage, anticipating your question, provides reassurance:

"This [usage] has nothing to do with egotism on the part of English-speaking people. Printing and handwriting have everything to do with it." When the Middle English first-person singular word "ich" was shortened to "i," the letter frequently became lost or attached to an adjacent word. Capitalizing the letter prevented confusion and error. No more danger of "i llewellyn, take thee Gwendolyn" turning mystifyingly into "illewellyn, take thee..."

On the subject of mystifying, Harper is the only grammar and usage book in our moderately extensive library that explains why I is the only pronoun that's always uppercased.