The system itself is proprietary. Not the practice of abbreviating common words of the english language. You can't copyright words. 1st ed. used these abbreviations, 2nd ed. did too. 3.0+ and D20 have as well.
I mean...if they COULD copyright abbreviations then they could copyright the usage of those things to denote human characteristics in a imaginary emulation of fictitious and fantastical conception.
As it is
C&C is practically D&D3E made a fuckton simpler. If I were to ever playing anything D&D I'd go for C&C over anything TSR or WotC any day.
If Troll Lords can get away with C&C I don't think we'll have a problem using D&D as a reference for a standard of abbreviation for stats seeing as it has set that precedent for over half a century now and been used by hundreds of other systems.
Well what is this that I can't see
With ice cold hands takin' hold of me
Well I am death, none can excel
-Ralph Stanley,
O Death!