Heh - but people prefer shorter words...and random is the closest, and may I add Most widely accepted variant - Heck, if people can get away with using it in an English Essay (As I myself have done AND not been questioned on), then that pretty much sums up that the Slang use is applicable, regardless of personal opinion.
Words and Dictionary explanations ALWAYS get bent over time, and language rules and ideologies are always constantly evolving - stay too rigid, and you'll find yourself simply getting annoyed too easily.
Reference:
http://dictionary.reference.com/browse/random - This also ties semi-neatly into the Slang-based definition...but this is merely one source.
More creditable and reliable sources can be found, However.
Besides, Since that it IS used as a SLANG definition, the word is taken out of the original context - 'Random' may be a mathematical term in and of itself dictionary-wise, but Slang usage is a whole other ballgame entirely. Essentially It SHOULDN'T matter if people use it as such, so long as the original use of the word is still intact for those whom would use it more in it's original state.
Regardless of what you might feel about the subject, this *is* the way of things now, and it's not likely to change just for a few who take up arms because they disagree.
But I digress...This is a thread about video games, and a discussion about language use is pretty non-thread friendly, heh.