What are "straight vote caucus states"? What does that mean? You mean primary states? Primary states have more than 1000 people participating (like who did in WV). There is no evidence that Romney can reach 50%+ in any state other than Utah, really.
I don’t think most caucus states require a candidate to reach 50%, I think what you get is what you get. That’s how Iowa, Nevada, Wyoming and Maine are.
I don’t know about the others. Romney has won all of them but Iowa, and came in 2nd there. West Virginia is the first I’ve heard that does the 50% rule.