Why did Yo'av gather everyone?
Radak: He wanted to see who is missing.
Are the 12 pairs who fought counted among the 19?
Malbim: Yes. Apart from them, only seven died from Yehudah, and about 50 times as much from Avner's men (verse 31). Such a victory in unheard of 1 !
I.e. according to nature. When Hashem helps Yisrael against their Esav, normally no Yisraelim die, e.g. against Midyan, Yericho
Is Asah'el not among David's men?!
Rashi: He was equal 1 to all of [the 19 others who died]. The same applies to "Re'u Es ha'Aretz v'Es Yericho" (Yehoshua 2:1) and "Shlomo Ahav Nashim Nachriyos Rabos v'Es Bas Pharaoh" (Melachim I, 11:1).
Radak: He was more honored than the 19, therefore he is not included with them, rather, he is written by himself.
Rashi (Yehoshua 2:1, from Sifri): He was as hard [to defeat] as all of them. Yericho is part of ha'Aretz; it was as hard [to capture] as the rest of the land, for it was on the border (so it was greatly fortified. There were many cities on the border! Malbim explains that they send spies to find the easiest places to conquer [to begin there - PF]! Refer to Yehoshua 2:1:7:1.) Bas Pharaoh was singled out among Nashim Nachriyos because he endeared her as much as all of them, and she made him sin as much as all of them.
