1) when did the "dead ball era end?"
2) when did the pitching mound get lowered?
3) when did the DH come into the AL?
4) are there any other changes (aside from baseball parks) that physically influenced the batting or pitching stats since 2) above? if so, when did they occur?
There have been quite a few things that have affected pitching stats since 1969, none of them are new (or altering of) rules.
The biggest change has been the focus on relief pitchers. Starting pitchers went from completing almost 30% of the games they started down to roughly 13%. Stadiums have moved away from the cookie-cutter parks and most new parks are hitter friendly. More widespread use of astroturf is a minor consideration but noteworthy. The strike zone was reduced the same year that the mounds were lowered and more strictly enforced (supposedly) starting in 2001.