1. Rudy Giuliani was under the gun in late 2007 for a lot of reasons that had far more to do with his personal actions and that of his associates than anything related to campaigning or strategy. His long time political ally in New York Bernie Kerik got into trouble with the law. There were accusations that Rudy had misused funds to carry on a personal affair, while his wife was ill or something salacious of that nature. And then he was out of touch with the GOP base on abortion, guns and immigration.
2. Rudy was not actually collapsing in New Hampshire. Romney had been dominating New Hampshire for months with around 30% of the vote, Rudy had been in the high teens and McCain was right behind him or tied. This only really massively changed, after he pulled out, started railing against the New Hampshire Primary and then he tanked into the single digits.
Even if you doubt my theory as to why Rudy pulled out, the established narrative of him "tanking in the polls in NH, fleeing to Florida" just doesn't hold up according to the most credible polling outfits at the time. At most he ebbed a little, but that was likely more to do with McCain's recovery than to a collapse by Rudy.
3. Pawlenty's major problem was Mitt Romney. They basically occupied the same "boring rich guy who is pushing for the border hawk vote" space. If Romney doesn't run in 2012, I think Pawlenty actually has a path in that situation.
You might be right about Giuliani and New Hampshire. But he definitely started imploding in Iowa the moment he set foot there. His positions were well known to most Republicans when he was leading in the polls. I think it's easy to say by now that the guy is a sleazy jerk and with a personality like that it's difficult to thrive in the arena of early state retail politics.
Pawlenty was not a rich guy like Romney. On the contrary, he ran as a working class, populist Republican, with his mullet and Sam's Club shtick. His biggest problem was that he was so booooooring. But people like Cillizza were convinced that he was presidential timber. It was so funny when he dropped out and so many DC pundits were despondent and couldn't explain what went wrong.