Many people don't remember this, but back in the mid 90's, when everyone was gearing up for someone to break Maris' home run record, the most common theory for the large increase in home run rates was that the ball was juiced, not hitters.
Unfortunately, especially for those who prefer things like "research" and "science" over speculation, once steroid-mania hit, that theory died a quick death. That death was premature.
There's is a growing body of evidence that there have been substantial and significant changes in the baseball used by MLB. Today, Tom Tango adds his observation to the mix, concluding that while expansion and changing ballparks do not explain the increase in home run rate, a changing baseball appears to account for nearly all of the change.
This meshes quite well with the findings of other researchers, who have claimed that there has been a physical change to the ball itself.
Steroids, unlike HGH, increase physical strength, no doubt about it. However, the link between steroid use and baseball performance is tenuous at best.
This is why the steroid issue frustrates me so greatly. The whole issue has become nothing more than a soap box for old writers and old commentators and old players to break out that old saw about how players used be tougher and smarter and more competitive. This has been going on since baseball began.
Yet, we don't consider any of the other possible explanations for the increase in home run rate. I'm not saying steroid use didn't have some effect on that rate. I'm saying we don't know what that effect is. The best available evidence is that the effect, if any, has been small.
There has never been a period in baseball that could be analyzed apart from the context of the era itself. If you want to look at unadjusted statistics, you must accept that they will always be tainted by context, regardless of the cause of that context. If you look at adjusted statistics, the reason for the context is irrelevant. The day that the majority of baseball fans realize this will be a great day indeed.