There are a couple of things to take from this article. One of those is the article does not address the fact the Iowa is a swing state that is going increasingly Democratic. Democrats have won the last 3 gubernatorial elections and Obama won Iowa by almost 10 points. Would a Republican, even a popular former governor, fare well in an increasingly blue state.
Another thing is that Branstad built his reputation as a pragmatic conservative who could get things done. There were many such Republican governors in the 1990's; they include Michigan's John Engler, Illinois' Jim Edgar, Wisconsin's Tommy Thompson, and even George W. Bush in his Texas incarnation when he worked with a Democratic Lt. Governor. Branstad worked with a Democratic legislature to pass budgets that included increases in the sales tax. Branstad also supported the lottery, and bringing casino gambling to Iowa. At the same time, Branstad never got the reputation as a crusading cultural conservative. As Governor, Branstad did nominate the justice who wrote the opinion that legalized same-sex marriage in Iowa. The article makes it clear that it is an open question as to whether the tea-party, christianist rump that is the modern GOP would even get behind the former Governor.
In the end I think this bodes well for Culver. Culver has problems with some in his own base and while he is not universally loved, I don't think he is universally loathed. I claim no special insight but my somewhat educated guess is that Branstad will not run because he will look at the Iowa GOP and see that his brand of pragmatic conservatism no longer fits with the party. What I think will happen is that Culver will win by virtue of the fact that he is not the primary scarred mediocrity that will probably end up coming out of the Republican primary.