Exactly, the less formal the japanese is, the more unspoken words are left to be guessed by the context...

Another interesting thing about japanese is that because of the lower number of different syllables it's easier to understand in situations when it's not possible hear clearly (like on mobile phones when the reception is not good). I've remarked on it when living there and had a researcher working in the field confirm me that it was the case (not to sure of the details but that was during a discussion on voice compression).