2000 Iowa Republican caucus
George W. Bush (41%)
Steve Forbes (31%)
Alan Keyes (14%)
Gary Bauer (9%)
John McCain (5%)
Orrin Hatch (1%)
I guess if we define "ages" as "the most recent Republican to win the white house", your statement would be correct. Bush won the 2000 and 2004 Iowa caucus. And of course, the most recent Democrat to win the White House (who is in power right now), started his presidential campaign with a upset victory over Hillary Clinton in the Iowa caucus.
I would agree if Gingrich fans said "the Iowa caucus winner doesn't necessarily win the nomination", but instead they're claiming that Iowa "only produces flukes" and "no Iowa winner has won the nomination in ages" when it reality about 2/3rds of the Presidential nominees started with a victory in Iowa, including the 2 most recent presidents (Obama & George W. Bush).
Well, of course he won the 2004 Iowa Caucus. He was the incumbent president and de facto nominee. I'm just wondering, though, what the track record of the Iowa Caucus looks like before the year 2000.
Does your theory hold up before then? I haven't googled to find the answer.