I guess I just have trouble accepting the idea that Obi-Wan was such a blithering idiot that he didn't know the difference between a year and a generation. That explanation, while yes simpler and shorter to write, strains credibility far past the point of being believable to me, so for that reason I'm unable to call it the simplest explanation. The idea that the Jedi served the Republic long before the peace which had lasted for the previous millennium is a much simpler explanation to me. Believe what you want though, and I will too. Hopefully someday this will all be definitively cleared up in the new continuity.