@spendius,
I would have thought that an ex-govenor would be preferred to ex others in the main. An ex govenor has long experience of carrying out tasks a president has to do. The selecting of office holders and advisers, relating to senates and congresses and communicating with the public, for example.
He has been where the buck stops on a smaller stage. An ex-speaker or senator or congressman or independent has no experience of that sort of heat. And a 4 year president has just that only more so. And a politicised First Lady in a two term White House has too.
Media are keeping Gingrich alive because with a runaway Romney spending on ads would tank.