That being the case, why would one protocol and one astromech droid make much of an impression on Kenobi? If you once owned a Maytag refrigerator, and ran across another of the same model years later, would you assume them to be the same?
C3PO plays a greater role in interacting with Kenobi in Revenge of the Sith, at least in the book. However, you're right about Kenobi's sentiments. The book makes it clear he much prefers organic life forms.