Hmmm
Further research would seem to indicate that "one" is a pronoun, albeit one that doesn't fit the usual rules.

So I may have been talking out of my arse. The apostrophe is correct though.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Tue 12 Oct 2010, 12:26, 1 reply)

So we're back to the question of why it takes an apostrophe.
I agree that it does. As I said, I looked it up in Swan's, and as far as I'm concerned, that's good enough for me.

I just feel there should be a genitive declension without the apostrophe.

It seems my post at the bottom of the page isn't the end of it after all.
( The Awful Puppy Bakery is still bored, Tue 12 Oct 2010, 12:35, closed)

Indeed
And you would appear to have some grounds from to argue your case.

Initially I thought you were a raving loon for thinking that "one" was akin to the "real" personal pronouns, but the more I think of it, it does kind of fit in with the rest:

I/me/my/mine
You/you/your/yours
He/him/his/his
It/it/its/its
One/one/ones/ones

Interesting.

Maybe it's because it's a fairly modern thing, and was added to the list a long time after Old/Middle English?
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Tue 12 Oct 2010, 13:35, closed)

GRAMMAR NAZI'S'S'.

(viciousal, Tue 12 Oct 2010, 15:33, closed)