True, he was arguably better in those two series, but as you said, the Mavs were somewhat favoured in both series. The other three were against reigning champions, twice, and against the so-called two best players in the NBA.
p.s though few will remember it, I think Dirk's best series ever was '09 Denver. He went against a formidable defensive frontline and shredded them with 30+pts, 11 rebs, and 50%+ shooting. Second I think is '01 Minny. Dirk was still a young player establishing himself, KG wanted to have him one on one, and Dirk absolutely toyed with him, putting similiar statistics to the Denver series. Whenever someone says KG is sooo much better, they have to look at that series over and over.