While the talmudic passage quoted above is certainly relevant in this case, I don't think that it is necessary to even resort to such a source in this case. According to it's own interpretive methodology, the question was flawed from the beginning.
The question was why the pasuq in Shemoth 21:28 needed to state "wa-lo ye'okhel eth besaro - and its meat shall not be eaten" when it was already stated in Devarim 12:21 that meat may be eaten when it is slaughtered "ka-asher ssiwithikha - as I have commanded you." So, either there is a contradiction between the two pasuqim (with one implying a prescribed manner of slaughter and the other indicated that it there is no such prescription) or the implication of "ka-asher ssiwithikha" is only that the animal should be killed, or perhaps just killed in a certain place, and not eaten while alive. Thus assumes the questioner. However, not enough attention was paid to the language of Shemoth 21:28, nor was the entirety of the Torah considered before jumping to a [mistaken] conclusion.
Notice how the language of the pasuq is wa-lo ye'okhel ("it shall not be eaten") rather than the usual wa-lo thokhal or wa-lo thokhelu ("and you shall not eat [it]"). This is because the pasuq which deals with the shor nisqal is not directing the prohibition of eating toward Jews. Instead, it is directing Jews not to either give it to a non-Jewish resident alien (i.e. a ger toshav) or sell it to a nokhri (a non-Jew passing through the nation, but not a resident of it). Thus, it says [to Jews] that the meat of the ox "shall not be eaten" (i.e. by others who are not Jewish).
How do we know this? Because of the explicit statement of Devarim 14:21, which says:
Lo thokhelu khol nevelah la-ger asher bish`arekha titenenah wa-akhalah o makhor la-nokhri ki 'am qadhosh la-Shem Elohekha...
Translation:
"And you [Jews] should not eat any nevelah (i.e. that which is improperly slaughtered or dies of itself). You shall give such [meat] to the ger (i.e. resident non-Jew) who is within your gates, or you may sell it to a nokhri (i.e. a non-resident non-Jew)..."
In other words, Shemoth 21:28 is instructing that a shor nisqal may not be made use of in any way - not by a resident alien, nor by those non-Jews who pass through your dwellings willing to purchase it.
As a side note, a ger toshav was a non-Jew who was subject to Jewish jurisprudence and governmental regulation in every way. They are often referred to in the Torah and many times are spoken of in the third person as people who are obligated in certain thing as well as prohibited from certain acts while living under the Jewish nation. (See MT Hilkhoth Melakhim Umilhhamoth 8-10 for a complete discussion of this subject.)
And this is what the statement indicates in Shemoth 12:49, "Torah ahhath yihyeh la-ezrahh wa-la-ger ha-gar be-thokhekhem - There shall be one law for the native-born and the resident alien who dwells among you." See also, Wayyiqra 24:22 and Bamidbar 15:16, 29.
As Rav Sa`adyah Gaon writes in his introduction to HaNivhhar Emunoth Wa-De'oth, most people arrive at false conclusions instead of the truth because they settle too quickly, do not search out a matter thoroughly, and base their conclusions on incomplete or faulty investigation. The Torah is not a document thrown together and rabbinic law is not a pollyannish connection of dots. Search it thoroughly and weigh all of its parts before assuming error on its part (has wa-shalom).
Kol tuv.
