Who says?
The "rules" we go by were largely made up in the last couple of hundred years and mostly based on trying to make English sound like shit Latin.
You cannot argue that "stadia" is the correct plural of "stadium" without then arguing that we should apply the rules of the language of origin to every word we use -- and we do not do that.
(Me, I'm not... in any way intoxicated, Wed 5 Jan 2011, 20:29, 1 reply)

But that's the point
the rules are skeletal at best.
However, when Latin nouns were adopted into the English language, their plurals were too. It is only in the last few decades that such plurals have been Anglicised and thus 'stadiums' entered the vernacular and ultimately the dictionaries. This is not down to rules being applicable, it's just piss-poor teaching standards in English and widespread dumbing down in the media which filters down into education.

Yes languages evolve, and so they should. But it should not be as a result of poor education in modern schools.
( sandettie light vessel automatic New Twitter - @bollocksreally, Thu 6 Jan 2011, 13:06, closed)