if expanding earth theory is correct [1-3] then every planet should had have cheese alike structure, thus cave system by default!
It does appear this way, yeah. @Soretna has talked about this a good bit before and made a connection about why there aren't huge holes at the polar areas, but instead it seems that there are thinner polar crusts. It must be some function of planetary formation. I really liked the images @deandddd and @soretna shared before from Mars. The ice there really is convincing of this vapor release zone from thinned porous ("cheese holes") pattern.