Why do sequels use Roman numerals?

[Lostplanet22]

Galaki said:

manuel said:

NiKKoM said:
Just be glad they don't use Kanji

3 in kanji is actually a bit similar to 3 in Roman numerals. (Just turned 90 degreees) :P

Roman: III

Kanji: 三

Or Chinese.

Second column is what everyone use.

Third column is like writing one instead of 1.

Third are for financial documents so people could not easy forge numbers.