1) Rashi (16b, DH k'Amitah) writes that we learn this from the word "Emes." Torah is true. In the same way that a Sefer Torah needs Sirtut, so too a Megilas Esther requires lines to be drawn on the parchment.

2) Tosfos in Menachos (32b, DH Ha) disagrees with Rashi because he maintains that it is not necessary to do Sirtut on a Sefer Torah. Instead, he explains that the word "Emes" refers to the Mezuzah, which Tosfos agrees requires Sirtut. The reason the Mezuzah is referred to as the "truth" of Torah is that it contains Malchus Shamayim. When we write or say Shema (the Parshah placed in the Mezuzah), we are proclaiming the Emes that Hash-m is the King of the World.

Kol Tuv,

Dovid Bloom