Home Runs in 1987: were the balls juiced?

1987 is the only season where this actually seems plausible.  Click this link to see all the data and a graph or simply look at the data below going back to 1980.  It's the percent of at bats (AB) on which home runs (HR) were hit.  1987 was the first season when it was at least three percent.  The 1987 HR rate has been exceeded seven times since but 1987 is years before steroids, etc. are generally considered to have been in general use.  1987 is between expansion of 1977 and 1993, so diluted pitching is not a factor.  The only significant variable left: the ball.  Maybe manufacturing was off a bit and the baseballs were juiced in 1987.

Year     HR/AB
2012 2.99%
2011 2.75%
2010 2.79%
2009 3.04%
2008 2.93%
2007 2.95%
2006 3.22%
2005 3.02%
2004 3.26%
2003 3.12%
2002 3.06%
2001 3.28%
2000 3.40%
1999 3.31%
1998 3.03%
1997 2.99%
1996 3.16%
1995 2.95%
1994 3.00%
1993 2.60%
1992 2.13%
1991 2.37%
1990 2.32%
1989 2.16%
1988 2.23%
1987 3.09%
1986 2.66%
1985 2.52%
1984 2.27%
1983 2.30%
1982 2.34%
1981 1.89%
1980 2.14%