I think that it could also be the game itself: Better computers and cameras (things like PitchFX), better scouting reports, and shorter outings by pitchers have all contributed to offense being down. You'll notice there are probably much less complete games than there were during the 80s/90s. With deeper bullpens and less reliance on pinch hitters, the advantage swings hugely in favor of the pitcher.
Basically, the theory goes that first time through the order (first three innings), pitchers have an advantage. Second time through, the pitchers have a slight, though significantly less valuable than the first time, advantage. Once the batters see the pitcher a third time, the advantage (fatigue & pitch tipping cues) swings into the batters' favor. In addition to this, we're squarely in a period of five-man (and sometimes six) rotations. Pitchers are typically given five rest days between starts, whereby they would typically get four in the 80s and four to five in the 90s.
The cumulative effect of these changes (along with park factors), along with advanced training for younger pitchers (more TJ surgeries & more successful surgeries), have swung the pendulum to pitching.
Yes, steroids has an effect, but it can't be as extreme as shown. Steroids are supposed to help with endurance/longevity, so they would have helped pitchers as much as hitters.
