EJ Fagan of It's About the Money with some interesting charts on run scoring through the years.
As you know, run scoring has decreased dramatically the past few seasons. You may think one reason for that is that bullpens are better than ever with all those guys pumping it in at 95 mph, or pitching more innings and thus allowing starters to go all-out while throwing fewer innings.
While starters are averaging fewer than six innings per start this year, the relationship between starters' ERA and relievers' ERA actually peaked back in the 1980s (in 1982, for example, starters had a 4.05 ERA compared to 3.43 for relievers). Of course, back then starters went deeper into games and more complete games were thrown, so bullpens only had to rely on a top fewer guys.
What's somewhat interesting is the difference this year is very close, at least by ERA: Starters have a 3.89 ERA while relievers have a 3.61 ERA. Going by runs allowed per innings, however, 2014 compares to the past two seasons. Relievers are about half a run better per nine innings:
2014 starters runs per nine: 4.30
2014 relievers runs per nine: 3.93
2013 starters runs per nine: 4.33
2013 relievers runs per nine: 3.88
2012 starters runs per nine: 4.55
2012 relievers runs per nine: 4.00
Basically, as EJ's charts show: All pitchers have been getting stingier in recent years (even with all the injuries to starters this year, they're allowing as many runs per nine innings as last year).