Taking a look at the wording on pages 10 & 11 of Men & Magic it is really quirky and awkward. First of all the order of the stats is random: Strength, Intelligence, Wisdom, Constitution, Dexterity, & Charisma. There seems to be no rhyme or reason to this order. It's not alphabetical. Not grouped in any meaningful way like physical/mental, or in order of importance.
Greyhawk mixes it up even more randomly: Str, Int, Dex, Wis, Chr, Con. Blackmoor doesn't really discuss abilities, and Eldritch Wizardry only touches on Dexterity with a lengthy addition to its effects in the game.
It is funny that this order remained like this and carried all the way through to 1st edition with one weird difference: Constitution and Dexterity are swapped. Why? Oh, just because. This little change seems to have first appeared in the Blue Holmes basic edition.
At least in 2nd edition an attempt was made to organize them by physical and mental stats: Str, Dex, Con, Int, Wis, Chr, but strangely still not alphabetical. You can still see the original order lurking in there. All recent editions keep this odd order. Shouldn't it be: Con, Dex, Str and Chr, Int, Wis? Or even better with mental first and then physical (M before P). This is mostly cosmetic and doesn't affect the game however it is just another example of the chaotic roots of the rules and as much as things have been polished and organized these little artifacts still linger.
Here's a little chart to make it easier to see:
What is perhaps most interesting about reading the ability descriptions in M&M (Men & Magic) is how little useful game information is really given. Their primary purpose seems to be to provide bonuses to XP for class prime requisites. Beyond that only cursory and vague game information is provided.
Strength. Does any RPG not use the term strength? Grab any random rulebook, I happen to have Symbaroum at my desk. Alright it uses "Strong" not "Strength", but basically the same word. Runequest uses it. Even GURPS with all its effort in making everything advantages, disadvantages, and skills uses Strength.
Intelligence. Alright, GURPS uses IQ which I always thought sounded a little lame, but nearly every RPG has a version of this stat. In Men & Magic a lot of leeway is given to the DM to adjudicate the player's use of this stat. If a player wants to do something clever the DM can just say his character is too dumb to think of doing that, sorry tough luck!
Wisdom. This is expressed in a lot of different terms in various RPGs, but really what word is better than Wisdom to describe this ability? In M&M Wisdom doesn't seem to do much of anything though, the book basically says its the same as Intelligence.
Constitution. Of all the terms this one is probably the least used in other RPGs. Usually something like Stamina or Endurance or Health. I have to say this is my least favorite of the ability names and I was very confused when I first encountered the game. I thought the player had to write up a constitution for the character that represented his fundamental principles! Hah, how silly I felt upon learning it meant the character's health stat and was just another number. In M&M this stat is given some meaty useful game purposes: bonus hit points and resistance to paralyzation and petrification.
Dexterity. A good enough term. I might prefer Agility, but no qualms here. This is certainly one of the most basic stats that all games use. This provides a lot of oomph to a character and especially with Eldritch Wizardry is expanded into the most useful ability. Perhaps overpowered even. Hard to not make this overly useful and balanced with the other stats.
In conclusion, not my most useful post here, but I've had these thoughts bouncing around in my head for a while and I needed to get them written down. I think the original six stats from the original rulebook are one of the best and most enduring elements of the game and I can't think of any RPG that does it better. While I've played a lot of RPGs my experience isn't comprehensive as I'm sure few people have played every RPG ever made, would that even be possible? Let me know what you think in the comments below or in discussions on G+.
ps. I did mean to mention the Size stat in Runequest which I always felt was clever and a much better solution to the Size relationship problem in combat. Early editions of D&D tended to complicate this with different damage values depending on small or large targets. Later editions have cleaned it up significantly, but still isn't the most elegant game mechanic. You could argue this is one improvement over the original six stats.
pps. The most obvious order for stats is just straight up alphabetical, because there isn't really any game mechanics associated with organizing them by mental and physical stats. So: Chr, Con, Dex, Int, Str, Wis.