Thewok's example was a poetry contest, so I assume the judges are poetry lovers. You wrote that if the player "composes and recites some beautiful poetry, than that's what has happened in the game". So now in the fiction, we have an actual beautiful piece of poetry produced by the PC. There's now a face-off against the quality of the poetry of the NPC. You can roll a random die to see whose is better, or the DM can decide that the NPC's poetry is inferior (and whose to say one way or another?). It's not that one way is wrong or right. It's just that one way is in-bounds and the other is out-of-bounds. Part of that, I think, is reliance (perhaps over-reliance) on die rolls and application of the rules *all the time*. In this case, I would probably just give the player an automatic success or a big modifier. Because it's a game, and I feel it inspires the player to roleplay more. A dinky +2 bonus just isn't enough motivation for everyone.
I'll admit I wasn't really thinking about the context of a poetry contest. (Why not, given what I was responding to? Dunno - my brain got switched to a different track between reading the posts and typing replies.) I was thinking of the production of poetry in a broader context (eg wooing, or otherwise impressing).My approach here would be to let the player decide whether they wanted to play it out. If they did, and produced great stuff, it would be inappropriate to make a 'how good is your poetry' roll; but there might be a case for making 'what is the impact of your poetry' check, eg Diplomacy or Bluff.
But I tend to think along S'mon's lines. (And I'm also influenced a bit by BW's Duel of Wits mechanics.) The real question in the scene seems to be "Who do the judges favour?". And that's something for which there are action resolution mechanics, which I tend to favour engaging. If the contest was being resolved as a skill challenge (the default 4e approach if something is at stake - if nothing is at stake, then free roleplaying will produce the result that a player who produces some tolerable poetry wins) then I'd be happy to treat a beautiful piece of poetry as one success in the challenge. (I've never done this with poetry before, but have done it with combat - ie winning a duel, in a certain context, has counted as a success in a skill challenge.) But other successes would be needed. And of course, if a PC produces the best poetry, but nevertheless (for some reason) loses the contest, that seems potentially interesting in itself. What was going on behind the scenes?
This also goes to bigger issues of scene framing. In the poetry competition, how do the other PCs (and players) fit in? I would likely have framed the scene so that the need to compose a poem is only one element of the overall situation. Which again means that a real life beautiful composition is contributing to resolution of only one component of the total situation.