Why does the Torah see fit to specifically prohibit the blood of Chulin? Why would we have thought otherwise?
Rashi and Ramban #1 (on Pasuk 22): To forbid it in spite of the fact that it is not sprinkled on the Mizbe'ach. 1
Ramban #2 (on Pasuk 22):: The Torah mentions the Isur of blood by Chulin, because it intends to exempt the blood of Chulin animals from Kisuy ha'Dam. 2
Ramban #3 (on Pasuk 22): Because we would otherwise have thought that, since, once they enter Eretz Yisrael, the blood of Chulin sheep and cattle will be spilt on the ground and not covered, it would be preferable 3 to drink it separately or together with the Basar 4 - even via Nechirah (by tearing them open) or Eiver min ha'Chai, to prevent contact with the demons. 5
Ramban #4 (citing the Sifri): The Torah finds it necessary to issue multiple warnings against drinking blood because they were passionate about drinking it. 6
Ramban: And the Torah, in Acharei-Mos (Vayikra, 17:11) specifically connects the Isur Dam to the fact that it is brought on the Mizbe'ach (See Ramban). See also Sifsei Chachamim.
See Ramban (Ibid.) as to why this was not applicable in the desert, nor to the blood of deer, gazelle and birds.
Ramban: The Torah repeats this warning later, 15:23, in connection with a B'chor Ba'al-Mum (Pesulei ha'Mukdashin), whose blood was initially destined to go on the Mizbe'ach
What are the implications of the phrase "Al ha'Aretz Tishpechenu ka'Mayim"?
Rashi #2: To teach us that it is compared to water and is therefore Machshir food to adopt Tum'as Ochlin.
Why does the Torah not require covering the blood of sheep and cattle, like it does that of wild animals and fowl?
Ramban: Because, whereas one tends to hunt wild animals and fowl in the fields and forests, 1 it is necessary to cover the blood in order to avoid contact with the demons who reside there, one Shechts one's sheep and cattle where they graze, near the town, where demons are not commonly found.
Ramban: Before transporting them into town.