The whacky 2008 election is given as an example of how early front-runners can fail. However, if you look at the polls, you will see that although Fred Thompson and Rudy Giuliani (the poll leaders in September 2011) faded, McCain was always hanging back there in the double digits. Jeb Bush, the guy who is supposed to eventually win (according to prediction markets), is only in the single digits. Only 6% in the most recent CBS poll.
It was easier for McCain to come back from the double digits than it will be for Bush to come back from the single digits. McCain was generally well liked and was considered a war hero. Bush has a lot more negatives associated with him because voters are tired of Bushes. McCain had a much stronger claim to being next in line. I think McCain was a better politician.
Thompson was one of those guys who the evangelical right likes to flirt with (because of his strong pro-life position) but had no support outside of that group. They later discovered Huckabee who was the better candidate. Giuliani was a genuine candidate who could have won support from the elites, but he was a lousy debater and had nothing interesting to say. Being pro-choice also hurt him with Republicans.
Trump isn’t like Thompson or Giuliani.
Perry was in first place in September 2011 but Romney was a close second and polled around 20%, and furthermore had a strong next-in-line aura, having competed well in the 2008 primaries.