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Yeah, it seems you're right.

http://travel.state.gov/content/travel/english/legal-considerations/us-citizenship-laws-policies/renunciation-of-citizenship.html

A person wishing to renounce his or her U.S. citizenship must voluntarily and with intent to relinquish U.S. citizenship:

appear in person before a U.S. consular or diplomatic officer,
in a foreign country (normally at a U.S. Embassy or Consulate); and
sign an oath of renunciation

Renunciations that do not meet the conditions described above have no legal effect. Because of the provisions of Section 349(a)(5), U.S. citizens cannot effectively renounce their citizenship by mail, through an agent, or while in the United States. In fact, U.S. courts have held certain attempts to renounce U.S. citizenship to be ineffective on a variety of grounds, as discussed below.

And interestingly-

Persons who wish to renounce U.S. citizenship should be aware of the fact that renunciation of U.S. citizenship may have no effect whatsoever on his or her U.S. tax or military service obligations (contact the Internal Revenue Service or U.S. Selective Service for more information). In addition, the act of renouncing U.S. citizenship does not allow persons to avoid possible prosecution for crimes which they may have committed in the United States, or escape the repayment of financial obligations previously incurred in the United States or incurred as United States citizens abroad.

You guys only found partial list of causes.

Causes of Citizenship Loss

U.S. citizens are subject to loss of citizenship if they perform certain acts voluntarily and with the intention to relinquish U.S. citizenship. These acts include:

Obtaining naturalization in a foreign state;

Taking an oath, affirmation or other formal declaration to a foreign state or its political subdivisions;

Entering or serving in the armed forces of a foreign state engaged in hostilities against the U.S. or serving as a commissioned or non-commissioned officer in the armed forces of a foreign state;

Accepting employment with a foreign government if (a) one has the nationality of that foreign state or (b) a declaration of allegiance is required in accepting the position;

Formally renouncing U.S. citizenship before a U.S. consular officer outside the United States; Formally renouncing U.S. citizenship within the U.S. (but only "in time of war"); Conviction for an act of treason. Persons Who Wish