nareik wrote:1) I think it could be partially linked to a 'real life' background of the models.
2) I suspect this my just be a theme thing.
That's probably as close as we're going to get to an answer.
Back when models were metal
GW didn't produce too many variations, and upgrades to plastic often followed the same pattern (though the generic Dreadnought pack now does come with the LA missile pack). So the fluff was written to support that. "Special" cases get their own kits now, like the Blood Angels dread pack that can build a Libby, Furioso or
DC dread, all with two
CCW arms.
As for jumping techmarines the Blood Angels have long been described as particularly fond of jump packs and flying things. The fluff in their codex books states they usually start a campaign as Codex standard (as far as they can with possible Death Company) but as squads take losses the Assault squads are easiest to fill up by moving marines from other squads to them - almost every single one is all too happy to volunteer for a jump pack. The techmarines seem to be no exception.