I am sure someone knows this -- in "real life" of course, if I have a pitching staff that puts a lot of balls in play (very few strikeouts) my team's defense is more important -- more chances to rob a hit or make an error.  Is that true here?  Or is there a set number of "defensive rating dependent" plays regardless of strikeouts (which is how many tabletop games, such as Stratomatic, are)?

I didn't bother to crunch the numbers as far as babip et al, but I have a progressive league team with a top notch defensive infield that over the last three seasons together has led to pitching numbers far exceeding what would be regularly expected.  Gene Conley doesn't win many Cy Young awards on this site otherwise.

Yes, it is true in WIS.  Every ball that is "in play" can potentially be converted from an out to a hit (by teams with bad range) or from a hit to an out (by teams with good range).  Likewise, every out can potentially become an error, etc.

Strikeouts are computed before errors and +/- plays in the decision tree, so yes, defense matters more for a low-K pitching staff.

The quick answer is that good fielding is always important.  Bad K pitchers get 3-4 of their 27 outs by K.  Good ones average 9-10.  Either way, between 17 and 24 outs each game are influenced by fielding, and low K pitchers get a few more chances to be helped by good fielding than high K pitchers do.  But the majority of outs in an average game come from the fielders.

The long answer...This is a "IMO" post.  I don't have access to the programming.  I could be wrong, but this is definitely the way I understand the sim

• There is no advantage or disadvantages to selecting pitchers with real life tendencies towards ground balls or fly balls.  The sim doesn't consider it.
• In the decision tree, it is first determined whether a walk occurs.  After that, whether a HIT or an OUT occurs.  If it is an OUT, the system determines if it should be a strikeout.  If it is not a strikeout, then the system determines what position the ball was hit to (Again, IMO.  I believe that balls are hit to positions for ease of programming.  This implies no "overlapping" by a player with outstanding range).  The range statistics for that player can change whether the hit was turned into an out (+), an extra base hit reduced by a base (++), an out turned into a hit (-), or an extra base (--).  And, of course, for outs, then the fielding statistic is invoked to see if an out was turned into a hit (or a hit into an extra base hit) because of an error. 

So, even on hits, good fielders can turn them into outs or reduce the bases on XBH.   

Two pretty good threads related to this topic:
http://www.whatifsports.com/forums/Posts.aspx?TopicID=457843
http://www.whatifsports.com/forums/Posts.aspx?topicID=354542

In the sim, an error, minus play or plus play is calculated after the out/ hit determination, so yes, just like in real life defense does matter.  However I strongly believes it matters less that in real life.

In real life BABIP falls within a relatively narrow range for most pitchers.  A pitcher that allows a lot of ball in play will generally allow lots of hits.  In the sim, a K is calculated after an out, so BABIP is meaningless and K rates have little effect.  It is true that in the sim, low K pitchers have more errors and minus play behind them, but this is offset by getting a greater number of double plays.

In real life a great range player might be worth an extra out every-other game over an average fielder.  In the sim, even under ideal conditions it is tough to get more than 40 plus plays and under nominal conditions you should expect less that 30 plus plays.  Basically this means in the sim, infield fielding percentage (except for first base) is way more important than range.  No player year exemplifies this better than 1989 Howard Johnson at shortstop.  He is a fire hydrant with a glove, but as long as he is well rested, he will never make an error.  In the sim, these affects basically cancel each other and he is probably close to average defensively.