It really is supposed to help with attachment in adoption, although he seems attached to you, 2 months is really a very short time as far as attachment. I stopped dd's bottle at 18 mos and she was home at 11 mos. At the time, I thought it made sense because she was somewhat older than is recommended for a non-adopted child, knew how to drink from a sippy cup, etc. However, I really wish I had done it longer in retrospect. You simply cannot do too much in terms of doing things to help attachment for an adopted baby/toddler, IMHO. It may seem like its not helping, but you don;t know that either. On the other hand, I do hear you that in some ways he seems to be ready. I guess, if I were in your shoes, I would not yet take the bottle away, but would let him have the other alternatives as well.
There is also a concept in adoption called "Family Age", which means that in a way your child's attachment age is the length of time he/she has been with your family. Your child's family age would be 2 months.
It may sound like I am pushing hard for you to keep the bottle...and I actually don't mean to. Just wanted to make sure you got this point of view as well.
lucky single mom to 20 yr old dd and 17 yr old ds through 2 very different adoption routes