We left off yesterday with a question: Tosfos says the term kiddushin applies to a woman because through the kinyan of kiddushin she becomes off-limits to all other suitors. Tosfos, however, says the term kiddushin cannot apply to an object, e.g. you can't say, "This talis is mekudeshes to me." Why not? Doesn't the talis become similarly off-limits to all others (there is now an issur gezel for them to take it) through the kinyan?
Those of you who are Telzers probably were thinking something like this: the act of kiddushin is the cause (sibah - the magic word behind half of R' Shimon Shkop's sefer) of two independent halachos: 1) a woman becoming one's wife; 2) the prohibition of her marrying anyone else. It is this second aspect which allows us to invoke the term "kiddushin," excluded from others. The same is not true with respect to other kinyanim. The issur for others to use an object is not an independent halacha, but is simply an extension of the definition of ownership. An easy proof that this distinction holds water can be brought from the question Achronim ask of why not apply to every case of safeik in dinei mamonos the rule of sfeika d'oraysa l'chumra - safeik gezel - and force the money to be turned over. Where do we get this idea of "hamotzi m'chaveiro alav ha'araya" from? R' Shimon Shkop explains that gezel is a function of faulty/false ownership. You can't claim someone is a gazlan or even a safeik gazlan unless you can first raise doubts about their ownership rights. Gezel is simply the absence of ownership, not an independent halacha. (For more on this idea, see previous post here.)
My son intuitively liked this idea, but I wanted a Brisker answer. Here's my two cents (the more I think about it the more I convince myself it's not that different than the first answer): the issur for others to be with a married woman is a function of the woman's status; it's an issur cheftza. The issur gezel on an object is an issur gavra on others -- the Torah wants you to not be a thief, not for objects not to be stolen. It's not kinyanim which "create" the issur gezel -- kinyanim merely create the metziyus, the practical context in which people can either ability to curb their desire to steal or to exercise power to take what belongs to others.
My son's rebbe had a different pshat in Tosfos that I don't understand. If I get a chance to ask him maybe I will update this.