Starters have also improved, but only down to .257 in 2013 from .270 in 2004. This is a startling drop, and is not a surprise considering the huge increase in strikeouts among relievers. Just as with the strikeouts, it is interesting to consider how much further this could go.
It doesn't seem possible that this trend could continue forever, but could relievers be holding the league to a .220 average in a few years or even .200. Something like that might trigger some kind of response to help the hitters like when the mound was lower after the '68 season. It is possible that this is as low as it is going to go, but we'll have to wait and see.