[etfb]

As another commenter here pointed out, it's preferred, not correct. This is the old prescriptivist vs descriptivist debate, as seen among linguists. (Disclaimer: I am not a linguist. I just read Language Log.) If you're fretting about the correct this and the proper that (prepositions at the end of sentences, "whom" instead of "who", and so on), you're a prescriptivist, and you may (note, I said may) be making up rules where no rules are needed. I prefer descriptivism (as in: "nauseous" now means the same thing as "nauseated", which is different from its old meaning of "nausea-making", because that's how it's used).

(Edit: "different to" sounded wrong. I could never remember which way that goes.)

[thanatropism]

So, the correct nomenclature here is "preferred" rather than "correct"?

Or is "preferred" a "preferred" word, but "correct" is allowable?

[dantheta]

As an aside to your edit, I have also seen "different than" used more and more often of late. I'm not sure if it is an Americanism that I was just unaware of. It's not that "different than" is wrong, it's just different from what I'm used to!

[etfb]

In Year Eight at school, I had an English teacher who liked to mix things up a little. One time, I was answering a question in class, and I used "different to" or "different from" or something -- maybe even "different than", I don't remember now. The teacher told me to stand up, then explained that there was a right form and a wrong form for this, and got everyone to pick sides -- "than" here, "from" there and "to" over there. Then I bamboozled him, because I noticed that the smartest girl in the class, a gorgeous lass who gloried in the surname of Snodgrass, had picked a different side, so I reasoned that she was more likely right and defected to the same group. The teacher was deeply annoyed that I apparently didn't have the courage of my convictions; my point, which I understood instinctively even at that age, was that embarrassing a student to make a point was a totally shit way to educate people, and if he was going to place such a high premium on game playing in class, he could call me Kobayashi Maru.

To this day, I still can't remember which is correct - "than", "from" or "to". But I can remember the look on his face, and the fact that after that he stuck with slightly less aggravating teaching methods.

[cokernel]

Yes, "different than" is an Americanism.

I believe that "different from" is most common across all dialects of English: http://alt-usage-english.org/excerpts/fxdiffer.html (Note: This only compares UK English and American English, not "all dialects".)

[aninhumer]

For the most part, I don't think these kinds of issues are caused by disagreements in linguistic philosophy. Most people are taught language in a way which encourages them to think in a prescriptivist way, and they simply never learn about descriptivism.

[etfb]

And thence comes most of the really stupid arguments on Facebook that aren't about guns or Firefly.

This is why I long to own a t-shirt bearing the words "Practising Peddant".