I'm inspired on Heavy Gear regarding the LOL Landcarrier factor, but then I got into the superior Mech Warrior series which were made of epic and win until M$ killed them, and not satisfied, r4ep'd Shadowrun
I have good reasons to not make a "wet" navy obsolete, other than the fact that in a planet with enough water for them to hover through or to submerge(and for human inhabitation), Solar Communes would rather take it over than destroy it at most if not all times.
http://images.gamersyde.com/gallery/pub ... 1_0005.jpg
Suffice to say their lack of access to gravitics because they were impossible under their universe was compensated by major breakthroughs in magnetic technologies.
Most inhabitable planets have a strong enough magnetic field to allow universal MagLev given proper technology. Basically its principle is like that which moves the pointer of a compass, only that due to a much higher magnetism from -unobtainium from alien planet- it uses the magnetic field to move thousands of tons of metal rather than a small pointer. Take or leave monopole magnets of the equation.
PS: Unless you consider a tracked(for smaller) or hovering(for bigger) vehicle with an AI and a turret almost as flexible as an human arm a mech, I don't have any mechs.
PS2: When you are invading a planet, a land carrier demolishing a city with its sheer mass is more intimidating and manlier than a distant spacecraft bringing death from above.
PS3: And blood-soaked World Eaters with chainsaw axes and melee weapons only are even more intimidating than any uber-tech.