They don't always do something SUPER-SPECIAL for the ten-year anniversaries but there's usually at least a little bit of special-ness there. Ten years: pitting him against Mothra, another popular Toho kaiju, Twenty: Robotic doppelgänger! Thirty: Revival after nine years! Forty: Remake of Mechagodzilla! Fifty: OH GOD, BLOW OUT!
Now, I think the latter two of those four movies are
terrible but it pleases me that Godzilla's never missed a tenth anniversary. I mean, I don't want anything super-special, I just want something good. In 2014.
Unrealistic, I know, but that's my stance.