I think the main difference is that painters take a holistic approach to a piece, where it's not enough that the parts are good on their own, the main thing is the whole.
I think that is only partly true, while I can work a lot on a single object, I also move from area to area as to not loose sight of the overall piece (especially during inking). I'm also not afraid of obscuring details I just drew if the overall piece requires it...although you always run the risk of falling in love with a particular object/piece/area and have to really force yourself to get rid of it for the greater good. But I do understand where you're coming from. At its core it's about making compromises and for a painter these compromises are fundamentally different from a line-artist.
This is why outline based approaches such as the one you seem to be taking make me nervous, because you work on the parts one at a time, instead of iterating the whole piece. Your method does make sure that all the parts look detailed n nice early on, but it says very little about how the piece will work as a whole.
Well, I make the
assumption that when I have a strong rough sketch that adding strong details won't take away from that. Of course that assumption is not always valid and a strong layout can very much be ruined by over-rendering. However, taking a line-approach does not mean that every part will be equally detailed. Again, we I compromises in this respect, but these compromises can be very different from a painter's.
If you look at this piece:

I have a lot of details, but there are also areas (like the trees on the left) where a lot of detail (or even part of the object itself) is removed or extremely simplified. This kind of comic strip-look is of course the ultimate playground for line-artists. And it is actually my preferred medium (black and white, no grays).
This is why I often have problem a with ink artist's work, where you have this huge bunch of details and shadows, but very little focus.
Well, inkers tend to be obsessed with a certain
noir-look that is heavy on blacks. When I do a black-and-white piece like the one above I can easily be accused of taking the same approach...but there's nothing more thrilling than making a piece that works without colors or values (well, for me at least). But I understand you problem, although I look at it differently.
There's also a difference - for me - when it comes to the final medium. Adventure games are background-centric. The player is a glorified cursor used to explore that background. In an animated movie/series it's quite the opposite: it's character-centric. The backgrounds are there to give a backdrop the the character's actions. Comics are somewhere in between. People are invited to explore the background at their leisure, but each panel is ultimately about the action/characters who's position you fully control. As a result, additional details that could be disastrous in animation might be beneficial in an adventure game: it's about exploring the background so adding actual details to explore will be in service of the main purpose. You also want to make sure that - even though you guide the player - the focus is not too much on a single area because part of the puzzle is finding the area of interest. On the other hand, you should also not obfuscate your area of interest by adding every little minute detail for the sake of details. That would basically be the same sin as pixel-hunting.
Of course there's also the technical aspect of having hard outlines and shadows with a universal ambient lit backdrop over soft edges, shadows, and shapes. It's simply much easier to integrate characters, walk-behinds, etc in the former to a level that truly fits the art(ist). That is not to say that it's impossible with the painterly approach. There is ample evidence of that. It's just a consideration/compromise I make; largely based on my background.
ps. compromises is the wrong word, it's more design-decisions.
edit:
pps. I'm always a bit torn whether these workshops should be part of the
competitions and activities, the
critic's lounge, or something else entirely. It kinda felt like it was cluttering up this area, but I also never thought there should be a special workshop section. Maybe with the micro-workshops my stance on this would change. But it's something to consider...