With things like Amoxicillin, Amoxicillin is Amoxicillin regardless of whether or not it is human grade or animal grade and yes it will be made in the same factories, on the same production lines etc.
Also when it comes to the shelf life of meds, I really wouldn't be too concerned, the use by dates are usually arbitrarily chosen by the drug companies, they of course do not want they drugs sitting on the shelf for years, they want you to throw them away and buy some more!!
http://www.defense.gov/news/newsarticle.aspx%3Fid=44979
BP does raise a valid concern though with regards to the purchase on meds over internet, are you really getting what you think you are getting?