Despite what Wikipedia says, I'm not convinced by the claim that people who speak tonal languages such as Chinese are more likely to have perfect pitch as a result of their native language ability. Having listened to a lot of tonal language speakers in Asia over a number of years (I even got quite fluent in one), I concluded that the rises and falls of the vowels are governed by relative pitch, not perfect pitch - and everyone speaks in different 'keys' (for want of a better word) depending on their age, size, gender and lifestyle choices, especially in the case of Bangkok Ladyboys who sound like they're speaking with the vocal equivalent of a capo at the third fret (overheard from a distance of course)
It's similar to the way we use relative pitch differences in English to express feelings, or ask questions, (e.g., Yes? and YES!!!)