"And Moshe spoke unto the heads of the tribes of the Children of Israel saying: This is the thing which the Lord hath commanded.  When a man voweth a vow unto the Lord or sweareth an oath to bind his soul with a bong, he shall not break his word; he shall do according to all that proceedeth out of his mouth." (Bemidbar 30:1-3)

Rashi on this section states that the unusual formulation of speaking to the heads of the tribes was meant to teach us that he was giving a special honour to them by teaching them halachos first and then the rest of our ancestors after.  As well it came to tell us that a single expert in vows can annul a neder just like a plain three-man beis din.  He then specifically excludes the possibility that Moshe Rabeinu, a"h, was only transmitting this section to the princes.
However, I saw written (by a roshei teivos I didn't recognize) that in fact this is exactly what we're supposed to get out of this special formulation.  Not that we should think that the rest of our ancestors weren't told all these rules but that the reason for the emphasis on the heads of the tribes was for a specific purpose.
This is especially relevant considering we are once again into a presidential election campaign south of the border.  As this source notes, when people are running for office they are quite quick to make any and all promises as to what they'll do if you'll vote for them.  Once they actually get into office, however, the promises are quickly tossed aside for various reasons.  Maybe the state's finances aren't what the politician thought they would be, or perhaps circumstances prevent some of the plans, or perhaps the politician is - gasp! - an old fashioned liar.  Perhaps what the Torah is hinting at is that leaders have to be accountable to their flock.  Promises, promises, promises, is simply not an acceptable strategy for achieving and maintaining a leadership position.
One must wonder what kind of shape the Western world would be if politicians running for office were to heed the Torah's advice and only promise those things that are in their power to fulfill.