Maybe that was just an assumption my part, but all of those little elements we get in the OT (that one's a master, one's a knight; that one is the superior of the other; that one teaches in different ways; that one might have had the skillset to train Anakin while the other didn't) were very important because, as zombie says in his book, Yoda was basically just a replacement Obi-Wan. They were, in essence, the same character. So you really needed those distinctions to separate them. But for some reason in the PT, all of those are done away with. Obi-Wan becomes a Jedi Master, so he's basically of the same rank as Yoda. Yoda fights with a lightsaber, so he basically does the same job as Obi-Wan. They're both wise Jedi. They both seem perfectly capable of training Anakin... or they both seem equally indept depending on which view you want to take. Really, the only differences that remain are superficial. Obi-Wan is a human, Yoda is a little green thing. Obi-Wan speaks with a British accent. Yoda speaks like Time magazine back in the 1930s.