Face the facts, there are far more registered democratic and Independents than there are registered to vote in GOP primaries.
In 2008 Ron Paul could not even pull in 5% of the GOP primary vote in any of the early primaries. And his later wins came only as a protest vote after McCain had locked up the GOP nomination.
This year, Ron Paul GOP is averaging about 20% of the GOP primary vote. Maybe impressive so far, but as various GOP candidates drop out, the new GOP question may become, can Ron Paul pull in 40-50% of the later GOP primary vote. And if and when Ron Paul wins the GOP nomination, the bar raises far higher, because the GOP voters are a minority, Ron Paul will need all GOP votes plus the ability to peel off enough independent and democratic voters to reach 50.1% of the general election voters.
So far, IMHO, the media has been kind to Ron Paul by basically ignoring him most of the time. While still granting him a soapbox to denounce our too aggressive foreign policy and other too big government issues.
But if the media and other entities start to really delve into all Ron Paul fibertarian fantasies, and what it would mean to the average American, Ron Paul support would drop to near zero.