Interesting site - didn't know this one.
One of the problem with most Pentax DSLRs is also the AA filter. Pentax has chosen an aggressive approach here thus many images are softer than they should be (except for the K-3 (II) and K-5 IIs). This is also reflected in the LW/PH actually - we will not push the conversions settings beyond a certain degree thus the max. LW/PH are comparatively low.
However, you can't blame the lenses for this.