He has pre-written material that someone else is posting on his behalf. He claims to have up to a year of blog posts written up on the event of his capture.
Occam suggests he IS writing the blog entries, and I'd say the GPS coords are accurate via the same reasoning.
And looking at the bigger picture, his behaviour suggests he was intimately involved in the murder. I don't know much about Belize's police force, but I would be surprised if he was at a greater risk of death by cooperating with them than by going on the run - particularly with his fame.
In fact his behaviour reminds me most of Charlie Sheen's drug-addled antics last year. Sad to see someone fall so far.
McAffee stated this in one of his earlier blog posts [1]. The blog is administered by a third party, and although a lot of the content is written by McAffee, most of it appears to be pre-prepared.