When I set set up my email account at google apps few years ago my MX records were messed up, so no mail could be delievered to my new google app address from outside gmail. However, my regular test gmail account was happily sending emails that were received on my apps account although MX records were messed.
Thinks might have changed in the meantime, but my guess is that Google still sends emails directly for accounts that it "knows" are hosted on gmail and apps and happily ignore MX records.
Thinks might have changed in the meantime, but my guess is that Google still sends emails directly for accounts that it "knows" are hosted on gmail and apps and happily ignore MX records.