Although I agree with what you're saying, Arowanna, a concept can also be
represented with just a front view like this:
http://perzo.deviantart.com/gallery/#/d4csatj
Anyway, to clarify:
An illustration where there is a message being conveyed (like the last image you linked) - usually with a background, a subject, perspective, depth, and a focus - is not a concept art, but there may be several concepts put together in this sort of illustration.
A concept art is initially not meant for public eyes. They are used to quickly represent characters, clothing, items, buildings, locations, etc. Makes less work for the other artists as it's easier to put together loads of concept art and deciding on a style from that rather than, well, buying new fabric to make a new costume because the old one wasn't quite there. Concept artists tend to "cheat" as in use bits and pieces from photos or other artworks. The point with a concept art is to illustrate the idea(s), and it's supposed to be fast to do. When you have decided on an idea, then you may go ahead and make something more polished.
We can't have people "cheating" on this site, because it's public. So the entries will be the polished result, possibly with orthographic (that is, front view and side view, and back view if needed) as well. What I'd like to see, though, is people posting their silhouettes and colour mock-ups as part of the whole WIP process. This could easily be implemented in the rules, but the inherent problem is that different artists approach this differently and demanding that people post silhouettes and colour mock-ups could seem an extra chore to them.
Lastly, a few examples of how a final entry could be in a concept art contest (from my favourites!):
http://fav.me/d36n5v8
http://fav.me/d2iv90b
http://fav.me/d45ju0f
http://fav.me/d3kyf6t
http://fav.me/d33fhzb
http://fav.me/d2oqp3j
http://fav.me/d2yi2tn
http://fav.me/d2q2g2k
The basic idea is full body, faint shading merely to denote shape and no fancy effects. You want to show what your character looks like, but you may also want to give it personality. The look takes priority.
Lastly, there shouldn't be much trouble making a concept in one month. If it takes longer, you're doing it wrong.