first note for you guys doing the cast:
play pikmin 2
second note, good show.
alot of the discussion on olimar made me post on this though, mostly because you pretty much all admitted to not playing pikmin at all (for shame

)
most important is the way olimar uses pikmin and how they act independently from him when thrown. considering all the fluff attached to the abilities and basic carbon copy of his moves from the pikmin games, i see no reason why the pikmin themselves should act differently.
when thrown, if a pikmin misses its target, it will sit on the ground in a neutral state. it wont even defend itself if attacked. the same thing happens if a pikmin is 'shaken off' an enemy. this will probably happen in brawl, too: if you miss, your pikmin will be prone, and when pikmin are 'shaken' or fall off a character after a set damage (im leaning toward the former, though the latter is just as likely) they will also become prone. the purple pikmin, as it 'slams into enemies' rather than latches, will probably deal heavy damage and knockback and simply bounce off and become prone, as well.
this is definitely where the pikmin will be attackable and able to be killed by opponents. i doubt they will be attackable when following olimar, but when prone they are defenseless. they can probably take damage when attacking an opponent, whose attacks will eventually shake them off into a prone state (or possibly kill them, which is just as likely). this leads to the durability of pikmin: it could pertain to how much damage they can take when prone before dying, or it could mean the amount of damage they can sustain while attached to an opponent before being shaken off or killed. the immunities are in most part fluff from the game, but the red pikmin will clearly be immune to fire based damage (marios fireball, bowsers fire breath, fire flower item, etc etc).
the pikmin callback special will, obviously, wake the prone pikmin and return them to formation behind you. the whistle has a set range however (see the glowy lights?), so if there are no prone pikmin in its radius, this is probably when the switch part of the move occurs. the whistle is a very fast move in the pikmin games, you are able to use it over and over in a short amount of time. i believe the whistle will be usable at the same sort of speed as the plucking (which seems pretty fast from the screenies). also note, that the whistle can call back pikmin that are attacking enemies as well, returning them to formation. timing will be a good skill to have when playing olimar, as shaken off 'prone' pikmin are open to attack, but called back pikmin may be immune to damage.
pikmin with flowers and buds in the pikmin games become faster and stronger. leaf pikmin move and attack slowly, while flower pikmin move and attack faster. i believe, in this case, that it will be a big part of olimars game to try to conserve pikmin as much as possible. this would mean alot of quick and frantic throwing and recalling, which will mean he'd need to stick pretty close to his opponents, so they dont kill off his more powerful pikmin and have him need to replace them with weaker and slower leaf pikmin all the time. this could be troublesome because olimar is bound to be super-light, and probably wont be able to take much punishment at all himself, so keeping pikmin between you and your opponent seems a big part of his game.
itll probably end up being canon to damage the enemy enough with your smaller pikmin and finish them off by throwing a purple pikmin, which id assume is olimars equivalent of a smash attack. olimar, on his own, only has a headbutt move in the pikmin games. its silly to assume this will be the only A attack he has, of course, but i dont believe he will be a character focused too much on his standard attacks, as he is, by background, incredibly weak.
anyway, thats the 'get to know your pikmin' lecture out of the way. all pretty simple stuff, obvious to people who have played pikmin. speculate away, keep up the good work.