This verse provides the most important potential contraindication for the hypothesis I have proposed. The analysis of the situation has required that the foreign villages or cities with which trade has been set up are communities that practice polygyny and that the women are being sent to those villages. The Book of Mormon is so consistent in calling all "others" Lamanites that many have supposed that the Book of Mormon neglects entirely those who were already on this continent when they arrived. Therefore, when Jacob says that the Lamanites do not have more than one wife, is he not directly disproving my hypothesis?
Clearly I don't believe so, but that still leaves this verse begging explication. I suggest that the reason is found in the multiple meanings of Lamanite, according to Jacob himself. Jacob tells us that although there was a collective term Nephite and Lamanite, there were still tribal name (Jacob 1:13). Of course this applies to the Lamanite as well. I suggest that the "Lamanites our brethren" was a specific designation Jacob uses to refer to the specific set of people who followed Jacob's brother. This would be in contrast to a generic Lamanite term that would be used similarly to the way Jews use the term "gentile." Therefore, Jacob would be saying that his brother and his followers did obey the command of Lehi while the Nephites (both literal and collective) had not.
Because Jacob is commending them for obeying a command from Lehi this can pertain only to those who would have received that commandment. Of the generic Lamanites there would have been just as few as of the literal Nephites. They may also have founded a village, but they cannot account for the larger numbers of people in the land that fall under the collective term Lamanite. Those others who were already in the land would have been under no such mandate, not knowing Lehi, nor caring about the commands of the foreign visitor.
Jacob's tactic is to make a very personal statement, contrasting the supposed unrighteous people of one of Lehi's sons with the supposed righteous people of Nephi. This very intimate parallel depends upon both the familiar connection and the reversal of unrighteousness/righteousness between the Lamanite and Nephite peoples.
There is certainly no love between Lamanite and Nephite, no doubt not the least reason being to armed conflicts between the two groups (though it is not clear in Nephi's description in 2 Nephi 5: whether Nephi uses the term as the collective or the personal meaning). Nevertheless, Jacob cites a very specific reason why the genetic Lamanites are hated; "... whom ye hate because of their filthiness and the cursing which hath come upon their skins." This matches very well with the original description of the Lamanites after the split between the siblings. In this context, however, what is most interesting is that this reason for "hate" is used as a literary synonym for unrighteousness. In Jacob's sets of parallels, he must contrast extremes. The Nephites certainly consider themselves as righteous, and Jacob will explicitly say that the Lamanites are more righteous than the Nephites. The only evidence that they should be thought of as unrighteous comes in the designation of "filthiness and the cursing which hath come upon their skin." However these external signs might otherwise be read they clearly have an attached meaning of unrighteousness - a meaning Jacob counts on to make his point.