"I was reading the ROTS novel, and one of the reasons why Obi-Wan left is that he saw Palpatine's shuttle approaching."
^^ Hmm interesting. Haven't read the novel myself. From your description though that sounds kinda like a wussy move for Obi Wan to just hit the road at the sight of Palps shuttle. If anything, you'd think he'd stay because seeing the shuttle would let him know that Yoda failed to defeat Palps, and so he might want to try finishing him off himself.