Becoming a trend? I mean, short series are the definition of small sample size. The postseason has always been closer to an exhibition than a true test of opposing teams' relative strength.
I think PW's initial post had more to do with the teams' season-long performance, though. So assuming that, here's the last 10 years of WS participants' OPS+, AL first, winners starred:
2014: KCR 91, SFG 99
2013: BOS* 117, STL 102
2012: DET 103, SFG* 106
2011: TEX 110, STL* 112
2010: TEX 98, SFG* 98
2009: MFY* 114, PHI 104
2008: TBR 101, PHI* 99
2007: BOS* 107, COL 98
2006: DET 99, STL* 97
2005: CWS* 95, HOU 90
2004: BOS* 110, STL 107
(oh what the hell, I'll do some more)
2003: MFY 114, FLA* 97
2002: ANA* 105, SFG 110
2001: MFY 100, ARI* 94
2000: MFY* 103, NYM 98
1999: MFY* 110, ATL 96
1998: MFY* 116, SDP 100
1997: CLE 111, FLA* 98
1996: MFY* 100, ATL 96
1995: CLE 116, ATL* 91
So my conclusion is, yes, KC and SF are the lightest-hitting pair of teams to make the WS since 2005, and the 2nd-lightest in the Wild Card era. Of course, KC's ERA+ is 114 (though SF's is only 100), it's not like they're flukes. Just not a lot of consistent flash at the plate.