What people sometimes fail to take into account when they look at Space shows/movies portraying ground combat and declare that they don't make sense is the question of what's lead to deploy troops in the first instance.
In Starship Troopers (the movie, not book) for example, the Mobile Infantry are deployed planetside due to the bugs 'going to ground' in deeply entrenched nests that need to be rooted out because the spaceborne weaponry was ineffective at penetrating that deep underground.
In The Empire Strikes Back, the Rebels have deployed a shield generator that is either impenetrable, or so strong it will take lots of firepower as a delaying action measure, leading to the Imperials deploying planetside as the longer they wait, the more of them will escape. This also kind of applies to Return of the Jedi, as the Rebel Fleet wasn't able to destroy the shield generators so a infiltration unit was jobbed off for the task.
Regarding Elite, we have so little information regarding small arms and planetary combat (beyond the fact it happens) that many assumptions would have to be made as to why you're putting boots on the ground.
Firstly, there's Asymetrical warfare, the type we see currently in Afghanistan and Iraq, with modern military units deployed on the ground to (i) win the 'hearts and minds' of CIVPOP and (ii) root out OPFOR with minimal collateral damage, as such events will push CIVPOP more over to the insurgents side. Rocking up in 4 Eagles firing dumbfire rockets into an installation isn't going to be conducive to this type of warfare. Whilst the more death dealing assets will be used, Infantry would still be needed to PID the target on the ground and provide accurate Forward Observer duties if the role required it.
Secondly we have conventional warfare, to take and hold a region of land. Now you're opponent who is on the defence is likely to have some sort of area denying measure, such as Empire's aforementioned shield generator or a strong AA presence which would render any advantage your space/air superiority a moot point. To regain your advantage, you'll need to put boots on the ground to locate/destroy those assets to allow you to field your fast air, and for all the talk of amazing satellite cover/drone flights, conversley your enemies ability to hide their assets will no doubt improve at an equal rate, and nothing is better at Recce than a man in a bush with a pair of binocs.
Now we've identified our reasons to put INF on the ground, they need supporting. As we know the key to modern or future war is going to be tempo (speed of action) so they're going to need to be able to move around fast. Now in asymetrical that's not an issue, because your fast air can ferry people around (assuming there is a negligble AA threat), so they're going to need vehicles to move around whether this is light 'technicals' (ie trucks/4x4's) at the bare minimum or heavier APCs/IFVs will of course need to be dictated by the situation, so you'll need both types of ground transportation to move your troops around (because, if you don't you risk losing the tempo whilst trying to bring a suitable support asset up).
Now our infantry are mobile and roaming the countryside as jolly green giants of death, intent on assaulting an entrenched position manned by the OPFOR infantry. At this point, Arty and of course tanks are potentially going to need to be employed as well as you're own limited AA presence to protect these assets whilst they remove the enemies AA so you can try to restore air superiority.
At this point we've only discussed 'teeth' elements of the land war. Behind these guys will be all the Logistics teams ferrying supplies/casualties/reinforcements back and forth from your landing point to try to ensure you maintain the tempo of your aggressive actions. Suddenly you're looking at an ORBAT that is not too dissimilar from a modern amphibious warfare unit, except that some of the units/assets are either in space or deploying from space instead of from the sea.
The Aliens Colonial Marines Technical Manual (a fantastic source of believable futuristic military nonsense) puts it best in a quotation
"There will always be a need for a man with a rifle to take and occupy ground."
No need for you to shoot me. I'll do it myself 
