In my experience the English spoken in Singapore is as good as that spoken anywhere, although my time in Singapore wasn't that long. My earlier comment has obviously taken somewhat differently to how I meant it.
If English is their first language, then yes, they speak English "perfectly" by definition.
Languages are a constant clash between its natural evolution and its rules (which came from past evolution)
If language hadn't evolved romance language speakers would be speaking Latin today, and English speakers would be speaking Anglo-Saxon maybe? (which themselves evolved from other languages)
