I'm still amazed, that the main interest is the portfolio of matingpartners ^^
RPG's sure have changed since the 90's ^^
I actually have a theory as to why this is. Granted, it may be partially because Jack does dating sims and such too, but I think it's more about giving the player more reasons to care. I mean, most rpg plots have been done to death or have parts that echo elements that have been seen in games before (Like, even if it's just a cave setting for a dungeon you'll generally get that 'it's been done' feel). No matter how original you try to be, there is going to be some comparison these days. That being said, I need a reason to get me past those feelings. If I'm going to play a game through to the end I generally have to care about what I'm doing and saving the world (or any grand, overused reason) just isn't enough for me anymore. Character relationships give me that extra reason. It makes your party members more than just people that help me advance the plots. It makes them your friends, lovers, or enemies (if they give you that option)-- people that you care about one way or the other. It also makes player's feel like it's their game since they got to chose who they ended up with and since there are options it makes the game really re-playable.
Games like Catherine, Witcher 2, Persona 4, Dragon Age, Princess Debut (this game totally rocks so don't judge me), Harvest Moon, Fire Emblem, etc. would not be the same without relationship options (Okay, maybe Witcher 2 would work without it since most of they're pretty much one night stands, but then you wouldn't know what a manwhore Geralt can be). The walking dead game plays with relationships really well too. It's not a dating sim (maybe a child raising sim though. lols) by any means, but it does change how characters react to you and provides enough variety to warrant more playthroughs despite the fact that it's a pretty linear game. It branches a bit, but the end is always roughly the same. And yet, you don't care. I know by the end I felt proud of my Lee. I had a personal connection to him and all of the relationships he developed over the course of his story. Lee remains very dear to me because of this.
Granted, there are a lot of games that don't give you those options and still manage to be fun. I love Legend of Heroes: Trails in the sky even though it doesn't let you decide who to pair Estelle up with because the characters are so likable and there are a lot of sidequests (not stupid ones like fetching and collectible quests thankfully) that help you get further into the characters since they offer a bunch of new and fun dialogue that are totally optional. Suikoden is a lot of fun too. You get options, but not really dating options. The fun from these games comes from the three types of battles, the ability to recruit 108 people, and upgrading your base. I guess my point is, as long as there is something there that rewards the player for doing optional side stuff it doesn't have to be choice of romantic relationships.
On a side note, I also like romance options because I almost always hate the main girl type (the sweet, gentle, stupidly optimistic, naive, hates violence, more important than everyone else for some reason, can't do anything herself so you always end up rescuing her -- even though they pretend that she's so independent -- type) games automatically try to pair the main character up with in games with no options. It really sucks when I like the main character. I'm always like whhhhy?
Aaaaanyway, I feel like I might have gone off topic and rambled. I hope that my point is in there somewhere.
More on topic: Them centaurs are smexy! :D