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A subtle little problem with K/9 -- (actually any per-9 stat) -- is that the numbers can change with ZERO difference in pitching performance, if you get a significant difference in defensive performance.
If the DEFENSE makes 1 additional out per game, what happens over a season?  Well, that's 162 fewer trips to the plate for the opponent.  But INNINGS remains a relative constant.  In truth, Felix K/9 has risen in 2009.  He has 207.1 IP today, while throwing only 200.2 innings in 2008.  He's pitched almost an entire extra game (based on innings), right?  Except, if you look at batters faced, he's actually faced 7 FEWER batters at this point.  After 7 more hitters, Felix will have faced exactly the same number of batters in 2008 and 2009.  If he were to get 7 consecutive outs to start his next game, that would mean exactly 9 innings more pitched while facing exactly the same number of hitters.  If he had exactly the same number of Ks, his K/9 would actually drop.
The better the defense, the lower the K/9 for a pitcher who fans exactly the same number of hitters per batter faced.  Better defense makes pitching Ks *appear* to decrease.
Same holds true for walks, only in reverse.  More defense outs, means fewer batters faced, which means BB/9 numbers improve.  An improved defense will make an identical pitcher *appear* to improve his control, (and his HR/9 numbers should decrease also).
Most of the time, this slosh is small enough that it can be ignored.  But, at the extreme ends, (best or worst defenses), it can be significant enough to inflate or deflate perceptions of the pitcher.  Bad defense can PREVENT a pitcher from getting through 6 innings, while good defense can make a pitcher appear to be an iron man.
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That said ... when a club enhances its defense, Ks, walks and HRs should ALL go down.  *EXCEPT*, the improved defense will tend to make pitchers throw with more confidence, which can lead to increases in Ks and HRs.  Bad defenses can make pitchers tentative, and lead to sky-high walk rates, but can potentially lead to fewer HRs.  The key here is the pitchers can (and will) react to the quality of the defense.  It's not always about TRYING to pitch to contact.  It can just be about not being AFRAID to pitch to contact.