They are at least consistent in that anything below mega is lower-case, and mega and above are upper case. As for confusing prefixes like myria (my? M?) they just got rid of them from the official list 
The original prefixes (deca, hecto, kilo, myria, deci, centi, milli, and myrio) were all lowercase, so that accounts for kilo.
Because mega means ‘big’.
This.
That’s a great point, thank you!
And that would indeed be pretty wacky, right? Pretty meta…
Well, yeah, that is the way they are properly written. I personally don’t see the need to capitalize the part derived from a person’s name. Not that I get to make the rules.
The reason for mega being abbreviated uppercase is pretty obvious to me. Namely to disambiguate from milli. A “MW” is a megawatt and a “mW” is a milliwatt. That’s also why micro uses a lowercase Greek mu rather than an ordinary single Latin alphabet letter.
Of the common prefixes only micro, milli, and mega share a common first letter. Damned inconvenient the Ancients didn’t work harder at disambiguating their number grouping words by having them all start with different letters. Idjits.
Unrelated to the above …
Considering how common this is, ISTM that should be “Grocers’ Apostrophe”; they all seem to use it. Certainly far more than just one grocer uses it. 
I normally don’t have much patience with pedantic complaints about the language, but yesterday, my own pet peeve showed up.
I was eating breakfast with my daughter, discussing plans, and she said, “So are you not going to visit that place?”
I had just taken a bite, but this was a yes/no question. I could answer it with a simple nod or shake of my head, or a thumbs up or thumbs down.
Except for my peeve: yes/no questions that include a negative in the main clause. They cannot be unambiguously answered with a yes or a no, or any gesture equivalent.
I have never encountered a grammar snob who objects to this form of question. Everyone consider them correct, and they are widely used. But if you genuinely want to remove confusion and ambiguity from English, get rid of these questions!
Or you could revive the old convention of using “yes/no” as unambiguous answers to these negative questions, and using “yea/nay” as unambiguous answers to the usual positive questions. However, according to Wikipedia that seemed like too much work even when it was in place, which is why I called it a convention rather than a rule:
This is a major pet peeve for people with medical conditions that leave them unable to communicate except through gestures. (Imagine having to respond nonverbally to a question like “You don’t have any allergies, right?”)
The problem of course is rooted in the questioner wanting to both deliver the question, and to assert which answer they believe a priori to be correct.
LHOD’s daughter is saying “I think you expressed that you aren’t going to visit that place. Please confirm my understanding.”
And Q.Q.'s “You don’t have any allergies, right?” is expressing “I know that most people don’t have allergies, so the answer for most people is “no”. But what is the answer for you?”
In a social sense what’s going on is them trying to structure the question in such a way that the expected answer is “yes”. Because it’s supportive to offer people questions to which they can answer “yes”, and it feels better to the questioner to have the answer come back “yes”; someone answering “no” is inherently offputting and amounts to a gentle rebuke.
In some cultures it’s an outright affront to answer “no” to an utterly unambiguous question even if “no” is the truth. Better (socially) to lie than to ever say “no”.
Language is about a lot more than Boolean logic.
Letterally? That is: by the letter. There seem to be religious believers who claim the Bible or the Old Testament or something is Godott’s word letter by letter and not one iota should be changed and they call themselves letteralists to make the difference (and express their superiority) with respect to the mere literalists clear.
Apart from that – and it is only a suggestion – I disagree with the OP’s premise: I don’t think English grammar or semantics are acceptable at all. They are a mess. But I don’t hate them, I have even learned to find them endearing and funny sometimes, particularly since I learned not to care about my own mistakes. My excuses to the taliban of rules that must be often grated by my chaotic approach, it is not meant personally.
One that always bugged me: “He must be spinning in his grave.” It’s meant to be a comic exaggeration of “turning over in his grave”…except that “turning over” in that context means “flopping around restlessly” (as in “tossing and turning”), not “rotating steadily around a longitudinal axis.”
If he’s not spinning, you can’t attach him to a turbine and create electricity. (It’s been awhile since I read through Dresden Codak. But I remember that.)
At the moment I am feeling desperate to find a way to stop the race to obliterate the difference in meaning between “empathy” and “sympathy”.
A very simple example, for those who may need it in this world where the word “sympathy” is almost gone:
~I am a woman. You are a man. If someone kicks you in the testicles, I am very sympathetic.
~If you are a woman, and you tell me your D&C was painful, I would be empathetic.
A simple way of putting it is that sympathy is feeling for you, empathy is feeling with you. They are different and the way empathy has been taking over is driving me crazier, not getting easier.
And both “close” and “closed” are adjectives, with completely different meanings. “Close” means “nearby”, while “closed” means “not open”.
Of course, “closed” is also a verb (past participle). The library close to my house was closed by the county, so now it’s closed"
It is odd, when compared with “open”.
I empathize with you.
Hehehe
This problem cropped up on the old panel game show What’s My Line. Because a “no” answer gave the guest another $5, the moderator, John Daly, would’ve rephrased your “no” answer to your daughter’s question as “No, your father is not going to visit that place, yes.” To avoid the confusion, Dorothy Kilgallen would’ve phrased your daughter’s question as “Is it correct to say that you are not going to visit that place?”
You have my compassion.