This may not be a popular answer (after seeing what everyone else had to say) but I'll throw it in the mix anyway. My ped (whom I love) was perfectly okay with taking the baby's lead. Both of mine were off the bottle and formula by 10 months old! (they do a finger prick test in the office to make sure there isn't an anemia issue, which would requre the extra iron found in formula/breast milk). As long as you are giving them healthy options, which it sounds like you absolutely are, then it's perfectly okay to begin the transition from bottle to real food! I wouldn't worry about it one bit - he's just a little bit ahead of the game, because no one is going to be on the bottle forever!
Think of it like this -- is it healthier for us, as adults to receive our nutrients from the source itself (real FOOD) or from a vitamin or supplement? From the source, of course. So, same holds true with babies - formula is a supplement and necessary when babies are too young to perform the act of actual eating. When they are able, however, it's actually healthier to receive nutrients from food rather than a supplement! (I'm a certified nutritionist/personal trainer, by the way)!
So, those are my 2 cents -- keep doing what you're doing because you're doing GREAT!