The more specific answer is that neckties are a by-the-book sacrifice that people make. Suppose I have two potential job applicants, one wearing a necktie and one not. The one wearing the necktie is likely to want the job more, since he obviously cares enough about it to wear the necktie. (We will take it as a given for the moment that no one actually thinks neckties are comfortable.)
In a sense, the necktie is being used as currency for the domain of desire. It represents one's level of interest in the same way that going to the trouble of obtaining a birthday present for an acquaintance does. The fact that it has no actual use to the recipient is orthogonal to this axis; "it's the thought that counts," after all. I don't agree with this sentiment, but thought is certainly a reasonable way to gauge how important you will be to someone.
This occurred to me a few days ago, when I was exiting keycard-locked Evans Hall during break. A man was coming towards the door; I held it open for him. He smiled and was grateful. It occurred to me that the man's appearance was a big factor in my deciding to do this; he was generally quite well-groomed. He was not wearing a suit or tie, but he had clearly put some effort into obtaining his clothing. He was wearing a backpack that seemed quite full.
The currency here is again time. Spending time improving my appearance does not in principle change my likely actions in any way; my action tendencies are, again in principle, the same whether I'm wearing a wife-beater and Bermuda shorts or a tuxedo. My morals do not change. However, the simple fact that I have the time and money to spend obtaining an outfit and primping myself is evidence that I am unlikely to do something like vandalize Evans. It's shorthand for conveying I'm not desperate; the better my position in life is, the less likely I am to do something that would, for instance, end me up in jail with a certain probability.
Consequently, I let the man into the building where I would not have let someone with scruffier hair and a less dignified carriage in. The necktie situation is similar; if someone has the time to prepare themselves for an interview, they presumably have fewer concerns with the rest of their life (relative to their concern with getting this job.) If I hire them, they are likely to be more devoted to this job than someone to whom everything else is sufficiently important to make an hour spent readying for this interview not a good use of time.
The necktie is therefore currency not only for social status but also for mental space. This is still strange, of course; the necktie has no direct impact on the fortunes of the company, which (assuming it's not PR or anything) are based solely on my actions and not at all on my appearance. In a sense, it's still the cynical arms race, where people are losing productivity due to conformity and social pressure. Nonetheless, despite the fact that there is no causation, there is correlation, and thus I must admit that the necktie is not altogether useless as a social device.
Writing with capital letters is similar. The key differences between mixed-case and lower-case are, I think, twofold:
In my own life, the times that I choose to use mixed-case are the times that I've actually spent some time thinking about the issues involved. This is almost never; living life by one's intuition and by the doctrine of immediate response is incredibly fun, and I like to think it's forward-thinking since ultimately life will come down to intuition and I should hone mine in the arena of youth. (I'm speaking here mostly of child-raising, I suppose.) Mostly that second reason is just back-formed, though. But I digress.
I'm not sure whether the external dichotomy has engendered the internal dichotomy or vice-versa, but the thoughts I have are all either in lower-case or mixed-case. It's very easy to distinguish. It falls more or less along the lines of vocational me versus personal me; certainly whenever I think about math it's in upper-case, and I would argue that things like this fall into the vocational category as well on some deep level. They're very different media.