A Mac user in California asked today where they could find the ș (s-comma) needed for Romanian in the OS X keyboard layout for that language. The answer is that this character happens to be on a key which does not exist on keyboards sold in the US (known as ANSI or 101 keyboards), but only on keyboards sold in Europe (known as ISO or 102).
The solution is to download and install an alternative Romanian layout. Two sources for one can be found here.
How could Apple do this? I don't have the details, but I think it may be because Macs sold in Romania have a physical keyboard labeled for use in more than one country/language in the region, which required some compromises in key placement. The ș wound up on the extra key, and the layout provided with OS X has to follow that, so Romanians in Romania can type their own language.