Sometimes R2D2 reminds of a loyal dog or some other pet that someone might compare to exceptional animals like Lassie, or Benji etc. etc. Now of course there are the "ordinary" droids which are pretty much forgettable. The same thing goes with animals, if there's nothing special about them, it's just another dog \ cat \ whatever. Especially if you take into consideration that droids aren't exactly "hated" in the saga, they're just not allowed into certain areas - compare this to earth, where animals aren't hated - they're just not permitted in certain places. This could also explain the lack of recognition between the droids and Obi-Wan and also the droids and Owen Lars. Would you recognise your old dog if he disappeared one day, and he came back 20 years later ( if that was possible )? He would definately look different. He'd probably act differently as well.