To exclude romance from D&D is to not be true to the source material. Almost ALL of the literary inspirations of D&D (INCLUDING the uber-macho Conan stories) feature romantic relationships of some kind. Arthur and Guinevere (and Lancelot). Bradamante (the female knight from the legends of Charlamagne) and Ruggiero. Tristan and Iseult. Conan and Valeria (and Belit, etc.) The list goes on.
The important thing is that DM never forces the players in engage in romance. He can make it a possibility, but should never just say "your characters are attracted to each other, play it out". But then, I prefer old school sandbox-style campaigns where the players can do anything they please without the tyranny of an over-arching plot.
In my experience, romantic relationships add a great deal to the role-playing experience. They don't even have to take away from old-school orc-killing and treasure plundering. After all, what better motivation to raid an ancient tomb than to present your lady (or man) with the crown of some long dead noble (complete with a curse to provide future adventure hooks for the DM). I've had players with romantic relationships that didn't extend to their characters, non-involved players whose characters where intimately involved, and couples whose characters were also lovers. It isn't inherently disruptive as long as the DM sets and enforces boundaries for acceptable behavior at table (no bringing outside fights to the game, etc.). And to repeat, a DM should never attempt to tell players how their PCs feel about other characters.
You make a reasonable case. But romance is really a question of the interior... which is why people who behave according to a 'logic' of romance appear to be behaving illogically to other people. The interior is made exterior in legends and novels because the narrator just simply tells you how the concerned parties are feeling, and what they are thinking. The same holds true in plays, because you have soliloquies and expositors.
But role playing games are basically performative. Your character isn't feeling a certain way because he doesn't exist (I'm not saying so because I think you don't know, only to lay my groundwork). Hence the only 'reality' to your character's emotions are those things which are submitted to the group somehow... role playing games are a group activity. How do you make exterior these phantom interiorities? You can say them declaratively, have your character give a soliloquy or weave exposition into his dialogue, or have your character behave in a particular way which discloses his 'feelings'.
The first, declarative mode is OK but there's only a certain amount that the group cares about your character's hopes and fears. So, "Konan is sweet on Aleena" or "Konan wants to have snu-snu with Morgan" are fine... but let's not waste a bunch of time with it, eh? And supposing that both parties are PCs... "We take a long walk on the beach" or "We do it" are probably sufficient.
The second, dialogic way is fraught with peril. Nobody usually wants to listen to a soliloquy, especially one delivered in the persona of a monosyllabic barbarian or whatever. Now, the method of expositional dialogue is not too bad, but again if it dominates the conversation how is it interesting?
The third, active way is probably the most interesting insofar as the player saying "Konan buys a bouquet of roses" or "Konan brusquely excuses himself from the table" can lead the other players to have to interpret these actions, so it becomes a little game. What is Konan doing carrying around a bouquet of roses and a plush Flumph? Why is he hanging around that resthouse down the street... who does he know who is staying there? And so maybe this leads to the other characters tailing Konan one night, perhaps thinking he is betraying them or holding out on them, only to burst in on an amusing scene.
But I don't see much more promise in it than those little vignettes. Suppose that two players exchange "knowing glances"... how does that contribute to the game? OK, their characters call one another "pookie" and "pooh-direbear"... beyond that, where is the added content? Sure, they could go into a long spiel about how their characters spend time together, or worse yet how they interact physically, but is anyone interested in hearing this? I just don't see what the gory details of romance could possibly contribute to the entertainment of the table.
