That page is misleading when it comes to Japanese text: UTF-8 sucks for Japanese text.
UTF-8 and UTF-16 aren't the only two choices within the whole world, which is demonstrated in their choice of encoding Shift-JIS.
However, if size is such a concern (eg for web transmission), text compression neutralizes the perceived benefit of region-specific encodings.
Shift-JIS' continued popularity has much more to do with change aversion than it does technical merit.
Some details can be found here: http://en.wikipedia.org/wiki/Han_unification
@byuu No it doesn't. Try compressing a SJIS text using gzip. Then convert it to UTF-8 and do the same thing. With a "perfect" compressor, there shouldn't be any difference since the information contents are the same, but unfortunately we don't have a perfect compression algorithm that hits the theoretical lower bound for compression.