The bacteria from old milk is very different to the bacteria from random toys etc that babies can put into their mouths. I don't understand what the rush is to stop sterilising bottles, at least the bottles are all in one place, nice and tidy and easy to find all the bits and you can say confidently that you know they're clean enough. I'm very thorough about washing up and rinsing dishes etc under running hot water but I still sterilise bottles as recommended.
This link is helpful and explains exactly why you should continue to sterilise bottles until at least 12months.
https://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=641§ionId=145