I think the abbreviation is generally based on which syllable is the smoothest when used. Aero (or air, for Americans) feels clunky and weird compared to plane, likewise hippopotamus and rhinoceros seem like they'd be equally clunky to grab from the end.

On the other hand, that might just seem that way to me because those are the abbreviations I'm familiar with. Certainly "tele" seems an awkward abbreviation for telephone, but (in England, anyway; Americans use tv) it works perfectly naturally as an abbreviation for television and only seems awkward to me because it's not the one I'm used to.