Four English words chosen with a truly random generator will obviously give 4 times log(<size of dict>) bits of entropy. Four English words that you came up with yourself is different. I'd choose "sky blue ice dawn" :)
The nice thing about this technique is that it's pretty easy to remember randomly selected words. But even if you think them up yourself, you probably don't substantially shrink the key space an attacker has to search through as long as you avoid grammatical structures and words that have obvious connection to you.
