I don't think they could use the logic that the real issues are in Iowa, that it's the heart of the nation. It's rather sparsely populated, and the morals and lifestyles are, more than likely, very different from say the East Coast or the Pacific Northwest or Florida. Why are they so important? I hope someone can enlighten us...
I visited Iowa for the first time in my life over Christmas, as my fiancee's extended family are all in Iowa. Small town, Iowa farmers. I went into it with a bunch of expectations, none of which proved to be true. These people are certainly quieter than my own family, but they've all got these wonderful wry senses of humor. And, they play a mean game of pool.
More seriously, I'm more comfortable with Iowa's role in the process than I would be if the same thing were done here in Texas or even out in California. The Iowa culture is, perhaps stereotyping based on my limited sample, less prone to ideological outbursts and thus more likely to reach some sort of consensus. I imagine they're somewhat more resistant to being pushed around and manipulated by outsiders (possibly explaining Dean's 3rd place finish).
The more I've gotten into voting security, the more I've learned about the cultural differences between states in the U.S. Would you believe that Oregon votes exclusively by mail? The fraud opportunities are astonishing (e.g., sell somebody your unmarked ballot and they can mail it in for you), but they don't seem to happen. Not because it's impossible, but because the culture doesn't do that. Try that in other states, and you'd get a very different outcome.
Also, keep in mind that the Iowans aren't selecting the final party nominee. Their main effect is to knock off several of the weaker candidates. We've still got five major candidates standing. I'm not saying that the whole rolling primary/caucus system is in any way optimal, but given the regional differences in cultures, the limited budgets available to candidates, and the limited effect of early decisions, the system actually works better than many other aspects of our election systems.