It's just implied that Obi Wan goes off to become a hermit because it takes a great deal of meditation to reach the point where you can become a Force Ghost.

It actually makes some sense that Force Ghost Obi Wan would haunt Anakin, teaching him this to try and get him to realise the Emp dawg isn't cash.

I'm sure it's plausible, I'm just having trouble putting it into my mental timeline. It's a sexy sexy concept though.