WM20 had Goldberg and Lesnar in their last matches in WWE
WM22 didn't really have any big story, but it was the final match for Tomko in WWE(he left the day after WM)
WM24 we saw the "retirement" of Ric Flair. He did end up wrestling in TNA, but it was his retirement from WWE
WM26 was of course the streak vs Career match and the last match for HBK
WM28 is next year and it's possible that it could be the last WM for Undertaker. Others were rumored to retire around then too such as Edge.
So is this sorta like a curse now or what? Even numbered WMs we're seeing someone retire/leave WWE.