The national GOP is relatively laissez faire and federalist with regards to the state affiliates. They're basically allowed to do whatever they want, and many of them decide that winner-take-all makes their state more important in the nominating process and gets candidates throwing down big bucks there. They don't even get more than a slap on the wrist (losing half their delegates) for pushing their primaries too early, in this case before Feb. 5th. The Dems have mandated proportional representation for all primaries and strip states who violate the nationally established calendar of all their delegates.
Personally, even though I'm a staunch federalist in matters of government, I think the GOP should follow the Dems' lead in terms of how delegates must be allocated. Proportionality would have made it likely that one or two other candidates would still be in this race and we'd be headed for a brokered convention, with Paul not far behind any of the others in delegates. Instead, McCain's 35% razor-thin pluralities translated into a massive lead, and Paul's 5-10% (more in caucuses and western states) of the popular vote translated into less than that as a share of delegates.