I have had time to spend playing in the latest update and I can confirm that the planetary bombardment effect is working as intended on all planet types. I noticed that you must zoom into the system your ships are bombarding, and wait for the missiles to make their way to the surface. For sure it wasn't working on asteroids before this latest update, but perhaps I was simply missing the effects on other planet types by not waiting long enough before?

In anycase, it looks real nice and especially menacing when you bring a whole bunch of capital ships in to obliterate an enemy homeworld, I just wish they didn't die so fast so I could enjoy the explosions more. I like watching those heavy bombs slowly make their way towards the planet until you see the flash and mushroom clouds.