well, milk and formula are pretty similar in a childs mind. at just one year old, he isnt going to really understand that "hey, now they put milk in my bottle". its more like he may notice a different taste to his "formula". whether milk or formula is in his bottle, if he wants his bottle, he wants his bottle. what they should have said was some babies have a hard time stopping the bottle, but that has nothing to do with milk or formula being inside. so instead of worrying about the milk issue, just wait until you feel you no longer want him on the bottle(whether it be a week, 6 months, ect, whenever you just feel its time), then start transitioning away. its great he takes the cup at meals though so keep it up.
now im assuming he still wants his bottle, but if he doesnt, and he drinks milk at 3 meals, and eats cheese, yogurt, ect, i wouldnt worry about his intake at all. just make sure he does get liquids of milk or water, but i would highly suggest to stay away from juice. my pediatric dentists all recommended no bottles after 2 and no binkies after 3. also bottles should be drank, not a sip here, a sip there, and of course, never at night. they also attribute juice as the number one cause for the large amount of toddlers with cavities.
also nuby cups are a nice transition cup or even straw ones. i offered a cup of milk or a bottle of water and let my daughter decide. she loved milk. i did the same thing when transitioning her off the nuby cup to a regular hard sippy. good luck, but really, i wouldnt worry, he isnt going to be 5 with a bottle:)