Tosfos (group of talmudic commentators) in trachtate Sanhedrin 56B, DH
(opening words) "awchal," makes this very point. The fact is (according to
Tosfos) that G-d prohibited the slaughtering of animals for personal non
obligatory consumption (slaughtering for sacrifices or clothing, etc., was
always permitted) but *permitted* the eating of animals that died some
other way.
Sincerely,
Yitzchok D. Frankel
Long Beach, NY