the Republican primary process is designed to produce a nominee as quickly as possible. Hence the preponderence of statewide winner-take-all primaries and party-insider-only caucuses. McCain was able to do what he did this year because of a crowded primary field, and because unlike in previous years, no establishment candidate had emerged. Forcing states to take the measures you describe would violate the Republicans' professed belief in states' rights. This is why many Republican primaries continue to use WTA while the Democrats have mandated PR.
The purpose of this system is to avoid a deadlocked convention, prevent long, expensive primary fights, and give the party's nominee plenty of time to raise funds for the fall campaign.
The Democrats have recognized the problem with such 'raidable' primaries, the Republicans should wake up to the problems, and close the primaries.
a fair number of Democratic primaries are open, including the pivotal New Hampshire Primary. Quite a few Republican primaries are already closed.