Because so much of the job search process is vague and undefinable (e.g., What is "fit"? What constitutes "passion"? What is that nameless quality that breaks the tie between two top candidates?), people love to fixate on small, concrete aspects.
To name just a few of the stories I've heard, there's the engineering firm that tosses out every resume not on thick, fancy paper; the university that won't hire a candidate who wears an unlined suit to an interview; and the hiring manager who eliminates any female candidate not wearing nylons.
The truth is, you could drive yourself crazy trying to anticipate and adhere to every idiosyncratic rule that someone might have about candidates, and that is NOT where your energy ought to be when job searching.
Keep in mind that for every hiring manager who only wants applications on thick paper, there may very well be another who thinks thick paper is pretentious and cumbersome. And the vast majority? Aren't going to care one way or the another.
Use common sense. Follow directions. Dress professionally. But don't spend half an hour Googling different opinions on whether or not you should wear cufflinks to an interview.
The time you spend worrying about what kind of paper to use or what kind of suit to wear is time that you're not putting into the most important things: creating high-quality application materials and preparing yourself for a stellar interview. When it comes down to it, for the majority of places you're applying to, that's what is going to carry the day.