Well, you never seem to read responses Yahtzee but I'll point out that there are JRPGs that depict exactly what your talking about. If you look back at games like say "Thousand Arms" or the more recent "Agarest War" titles, these games both include ongoing romance plots/dating sims along with the RPG adventure stuff. Of course it's a no win scenario because chances are any game that included what your talking about would immediatly be shredded by you for being "creepy" and a form of entertainment for nerds who have never enjoyed any kind of female companionship IRL.
To be honest I also think your missing the point that most games are about stuff happening. A deep relationship starting makes a good "happily ever after" ending to explain what happens with the hero when it's over. A dedicated adventurer, or someone intending to take down an uber bad guy (or group of them) is quite probably going to want to avoid seriouis romantic entanglements, family raising, and other assorted things until it's safe to do so. I mean if by definition you feel the need to spend nearly every waking moment questing towards some purpose, your not going to be able to reliably stay at home with the wife and kids. Some people aren't douchebags and wouldn't make that committment knowing that couldn't honor it, and game heroes tend to be noble on most levels, and that kind of goes along with it.
Now granted, heroic fantasy only covers so much ground, and that's the fuel for games. That genere is used, because it works for the core experience people want. It's also important to note that in real life people can, and do commence relationships, including gamers (Lol!), the point of gaming is to vicariously do things you can't do IRL. It's about the pursuit of unreality in order to get away from reality. As odd as it might sound, your more likely to take a real girl out on a date, than say fight aliens with futuristic weapons.
At any rate, my suggestion is to look towards the dating sim genere if this is what interests you. You know, games like the one that Japanese guy apparently married. There are also a few hybrid games I mentioned, and if you can get past hypocricy in screaming "creepy" for doing what you want, they are okay, but I don't think anyone has ever gotten the idea to "click" properly and that's why you see less of them.
I think the odds of seeing a game seriously developed along these lines and succeeding is roughly on par of seeing high quality, mainstream game titles released with hardcore lesbian bondage romance/sex/love scenes for pervs like me. >
Oh and one other one. In "Alpha Protocol" two out of three of the potential love interests are likely to live to the end of the game. Who, if anyone, is waiting for you in your boat at the end is one of the variables in the game. The romances here being dependant on building relationships due to selecting the right kinds of dialogue options at the right time. Now granted, that doesn't sound like a lot, but consider the current technology. It's not like we have virtual "designed to be seduced" AI programs or anything.