Well, I wouldn't fully place Dimitri under this since it's not like he actually feels complete and utter kinship with everyone. (I mean, Yuki bugs him, Soren's comment rubbed him the wrong way, and seeing an entire squad of dead soldiers didn't exactly provoke the most empathic of reactions) There's a difference between a character who plays nice to avoid trouble and someone who's a genuine Messiah 24/7.
Besides, Fay is/was a friendship freak who completely puts his little peacemaking efforts to shame, so...
Very true about the duck pond, though to be fair we didn't exactly drive anyone off with angry quacking, they just kind of...dropped out on their own accord. =O
Erm...yeah, if I saw something of decent quality with even a little bit of innovation to it (and which hasn't started yet) I'd probably lunge at this point, but sadly there are none to see. .__.
True enough, as not all characters are wordy, but there's still tone and expression that can be addressed in the 'short replies' case without going out on a completely ridiculous tangent. The character's emotional reaction to whatever the question is, reasoning behind the decision etc. (unless, of course, it's something completely trivial like "Coffee?") are another source of material. The problem with writing a post that is just "yes" is that...well, what the heck is anyone supposed to give in response to that? "Okay, then."? Short posts without any details to pick up on only lead to even shorter posts as the less detail you give the less the next IC writer will have to work with, requiring more creative work on their side to compensate for the lack thereof from the other's. :\
Anyhow, the situations where the amount of topics that you can reasonable address has really, truly, honestly been reduced to a 'yes/no' prompt is usually one where two RPers have gone on a posting spree and left everyone else behind, in which case it's time to cool your jets and let others add to the story too. =O
Good point all the same, I'll have to address that in the guide that Loki already mentioned. (Way to go adding performance pressure J/K)
Seconding the attitude thing. If you just join an RP on a 'meh, why not?' mindset then you're most likely not going to be posting very much (or well) for it either, whereas if you join in in with fanpersonish fervor then you'll most likely also be checking up on the RP frequently, thinking stuff up outside of the time when you're writing, and just generally be more motivated for it. For me, whether or not I'm happy with the character I signed up is also an important motivational factor, hence why I always take so long to type out my profiles. :3