Parashat Matot-Maasei, 5775/2015 thought, slightly belated

See these previous posts of mine:
~ Parshat Matot (2011)--How did the half-tribe of Menashe get a free ride?
~ Parshat Matot-Maasei (2012)--An Ir Miklat/City of Refuge was the functional equivalent of "house arrest" and/or protective custody.

And now, for something completely different--on the subject of vows, as discussed in Parshat Matot 30:2-17, I refer you to Parashat Kedoshim, Leviticus 19:14:

יד  לֹא-תְקַלֵּל חֵרֵשׁ--וְלִפְנֵי עִוֵּר, לֹא תִתֵּן מִכְשֹׁל; וְיָרֵאתָ מֵּאֱלֹהֶיךָ, אֲנִי יְהוָה.

14 Thou shalt not curse the deaf, nor put a stumbling-block before the blind, but thou shalt fear thy God: I am the LORD.

In a recent discussion of halachah/Jewish religious law at Mechon Hadar (or perhaps it was on one of his Responsa Radio podcasts), Rav Ethan Tucker happened to mention in passing that a person can "take a vow" to become a vegetarian.  Exactly when in the development of halachah did the simple act of making a major decision and/or performing an action on a continuous basis become a vow?  And how?  And why?  Isn't the very definition of a vow, from a halachic perspective, a promise made to G-d, or at least, in G-d's name?  Where does G-d come into play in a decision to become a vegetarian?  Or to eat only fish, but not "fleish" (meat and/or poultry)?  Since when is such a commitment made to G-d, or at least, in G-d's name?

Speaking as someone who did not receive a yeshiva or Jewish day school education and who has a husband and many friends in the same boat, I think this is a classic case of "lifrei iver lo titen michshol (in front of a blind person, did not put a stumbling block"), as interpreted by the rabbis of old:  " . . .  one should refrain from tempting a person to sin or  leading a person to sin out of ignorance."  How many of us non-yeshiva graduates would have any idea that we would need to have our "vow" annulled if, for example, we realized that being vegetarian was incompatible with our personal metabolism, and that we would have to eat meat in order to be healthy?  It would never have occurred to me that a decision to become a vegetarian (and, presumably, at least some other major decisions) constituted a vow if I hadn't heard Rav Tucker mention it as an example of one.  And surely my generation is not the first in Jewish history to include amei ha-aretz, Jewishly-under-educated Jews--the rabbis' own definition of "iver, blind"--so they should have known better than to assume that every Jew would understand.

I honestly forget whether it's the Written Torah itself or the rabbis of old that/who caution(s) that it's better to avoid making a vow than to break one.  Yet rabbinic law seems to have turned decisions into vows even though no actual vow was made!  In all seriousness, does an adult man who's been wearing a black hat, black suit, and white shirt all his life need to get permission from a Bet Din (Jewish religious court) to switch to a s'rugi (crocheted kippah), blue suit, and yellow shirt?  Why would the rabbis go out of their way to create a category of sin where, to the best of my admittedly-limited knowledge, none existed previously?  (Is this what's called a "chiddush," an innovation in halachah?  Or is it a chumrah?)  Am I missing and/or misinterpreting something?