What this means is that it's actually getting worse!
The moderates who don't care one way or the other didn't matter, anyway. The moderates (so-called mainline) are in decline. But the extremists (mostly in the "evangelical / born-again" group) stayed the same as percentage of overall population. A whopping, frightening 40%. This means that percentage of extremists amongst religious people have increased. This also means that in religious circles extremist views are becoming more mainstream. It means that the moderating influence of formerly mainstream groups is declining.
For example, consider that the Catholic church for a long time already is very open and ok with science. Catholic schools don't teach any creationism nonsense. However, the number of Catholics is in decline (and would be even more so if it weren't for immigration). Now with the decline of the number of Catholics, the voices of the extremists are getting relatively (!) louder in any discussion that involves religion: State lawmakers, local school boards deciding what goes into biology text books, etc. Their voices are heard, their views considered.
Overall, the poll is very disturbing: It shows that the number of dangerous extremists (people identifying as "evangelical or born-again") has remained the same and is growing in importance within religious circles. This is a dangerous development.
Rationalists and atheists should stop focusing on the mainline religions, since they are "mostly harmless" these days and could possibly provide an outlet for those people who seek a spiritual component in their lives. Instead, with the decline of mainline religions, people are sucked in by the extremists. The extremists, however, are the dangerous ones that we should focus on.