DVD subtitles

I noticed something on the DVD. On the subtitle language selections, there an option of Mandarin and an option of Cantonese. Now, Mandarin is basic Chinese and Cantonese is a dialect of Chinese. The difference between Mandarin, Cantonese and any other dialect of Chinese like Taiwanese is in the pronunciation of words. It's like how pronounciation and lingo differs in New York, Boston, and Texas. There is absolutely no difference in written Chinese between the dialects- it's soley in spoken Chinese. The only difference is between traditional Chinese (still used in Taiwan) and Simplified Chinese (which is what is largely used in mainland China). As such, the subtitle track for Mandarin and Cantonese is identical (I checked) so there's no need for two different tracks.