What this demonstrates is that Democratic governors are responsive to voters' ideology; the more conservative the state, the more conservative governors' stances. Conversely, Republican governors appear to be completely unresponsive. No matter how liberal or conservative their state, they are advocating a strict conservative doctrine on a broad range of issues.
This graph reminds me a great deal of one that I produced for my book, comparing the ideal points of California legislators with the partisanship of their districts:
There's an important distinction here, though: in the California scatterplot, it's the Democrats who appear to be totally unresponsive to district sentiment, while Republicans actually behave more moderately when they represent more moderate voters.
One of the things Hans Noel and I argued in a recent paper was that a majority party would tend to have elected officials that were more ideologically extreme relative to their voters than the minority party would. There is an incentive, we argued, for minorities to moderate in an effort to win back control, while majorities seek to push their advantages to achieve as many of their policy preferences as possible while they're in power. If this applies to governors, as well, that's pretty interesting. After all, governors aren't really part of a national legislative chamber, so sticking together doesn't really produce an obvious policy payoff.
There are a number of reasons why the current crop of Republican governors might be more extreme than their Democratic counterparts or than Republican governors in earlier years. 2010 really was an unusual election. But what the above graphs demonstrate pretty clearly is that while the parties may be equally extreme in the long run, this extremism varies significantly by party from year to year. Sometimes Democrats really are more liberal than Republicans are conservative. Right now, it looks like the Republicans are the more extreme party.