Some of the rankings for Deep South states are pretty misleading (particularly showing the Republicans to be relatively moderate there) in my opinion. For instance, in Alabama, Governor Bentley (and many GOP state legislators) have been aggressively pursuing excise tax hikes in order to raise more revenue for roads and to a lesser extent, schools. This is because in many of those Deep South states, revenue is historically lower than in other areas. What's the upshot? Raising taxes in the Deep South is a very different action than raising them in a higher-tax state with more existing services. So these "moderate" GOP legislators in Alabama/Georgia are just acting on necessity in order to keep up basic services like infrastructure and education to an acceptable level.
The reverse happens in the minority party in a state. In the minority party one has little control over the major legislation brought to a vote. As a result the votes on a scorecard tend to reflect legislation far from the minority party's core interests. That tends to push their record more towards the extreme.
Interestingly, these current ratings seem to show Deep South Democrats (in Alabama and South Carolina) as very moderate. I wonder if that's because the scorecard reflects "NO" votes on tax increases as necessarily a conservative vote, even though in reality, the Democrats there would have simply favored a more progressive tax increase (or simply a larger one to raise more revenue).
