it all goes back to speed. think the train job episode of Firefly-- how did they get to the train? they had a spaceship that could fly much faster than the train, hopped on board, and loaded up the booty. imagine if the train had been flying, and jerked up-- it would have crashed the smaller ship and blown up the crew. Jetpacks would be great-- but the speeds are enormous; 1000 kms is really effing fast; voyager 1 (essentially the fastest man made object) goes what, 17 kms? If you and your house were moving at 1000 kms, and you slowed down to 999 for just a tenth of a second, the back wall would smack into you, you'd blast through, and would be splattered over several city blocks.
I'd posit that in only damaging the marines in a failed drop, steve is being nice-- a failed drop should be considered a ramming attack on the dropship with the potential of catastrophic damage.
on the other hand, space marines with jetpacks are awesome (Orz!)
