I've speculated that he's got a better chance of winning as an independent than as a Republican. For one thing, he wouldn't have to go through the primary process. Secondly, he would be able to credibly run as a "conservative" of sorts even while distancing himself from the Bush administration when it suits him to do so.
Ping to #95.
The history of the last several decades suggests that running for president on an independent line is a sure recipe for losing.
Why should he worry about the Republican primaries when, at least for now, he is the leading candidate? It's still too early to say what will happen a year from now, but it would be politically stupid for him to declare himself an independent or suggest anything of the kind now, to say the least.