Agreed with Carson about GW not being very original in almost anything, but neither do they hide the fact so It does not bother me.
Although starship troopers and space marines have absolutely no similarities at all in my opinion. The starship troopers are just normal people, not even augmented, they would be guardsmen if anything.
Space marines are super human, their models, and often codex/dodgy black library fluff completely fails to portray the huge, powerful creature that they are. More suited to terminator and bionic woman/million dollar man type references not so much because of regeneration (which they are quite capable of, knife wounds would visibly heal or fail to inflict any serious damage Hollywood style, while anything short of death can be fixed in their med "labs" or bionic upgrades, but their sheer power and unstoppable physique combined with the very best of military training and hardware.