To daven or not to daven

Yesterday I was amused in shul as davening, which usually begins exactly at 6:55, was delayed slightly while the rabbi worked out the question of who should lead the prayers.  After a string of Yahrzeits, I seem to be back "at work" as the Shaliach Tzibbur (prayer leader) at morning prayers.  However, yesterday was Shushan Purim, the second day of Purim.  While not celebrated as a holiday other than in Jerusalem, it does carry an element of simcha (joy) and, as such, the Tachanun prayer is not recited.  I figured I would be chosen as prayer leader by analogy to Tu B'shvat, another day when Tachanun is omitted but I nevertheless led the prayers.  I've also led prayers on the occasion of Brit Milah (circumcisions), when there is also no Tachanun.  Even the Rabbi was unsure whether Shushan Purim carried enough of an element of joy to disqualify me from acting as prayer leader.  After some consultation, it was decided that I would not lead prayers. The ruling was that since L'minatzayoch (Psalm 20) is also omitted, my chiyuv (obligation) to daven was not present.  I enjoyed that the community cares about these small details.  Everything matters.  Nothing is left to chance.  That's the way my mother lived.