This first occurred to me after reading Scipio's post from March 26th about Superman being essentially a circus performer, while Batman is more representative of the theater. At the end, he brings up how Dick Grayson, as Robin, represents an intersection of the two This isn't the first time I've read someone discussing that (though it was the first time in the context of theater vs. circus), but it set my mind to thinking about Grayson a bit, and I wound up wondering whether his romantic partners are intentionally following this pattern.
(I should point out, this is going to follow pre-relaunch continuity, at least as far as I understand it, because I don't know what's in play in the New 52.)
From my perspective, it seems like Robin/Nightwing's two primary love interests have been Barbara Gordon (as Oracle), and Princess Koriand'r (Starfire). One is an Earthling with the will to use her brilliant mind as a weapon against crime, as well as to train herself physically to be a more than capable combatant (even without the use of her legs, Oracle was far from helpless). The other is an extraterrestrial with considerable physical power (drawn from stars, no less) from a world that has been destroyed. Admittedly, not when she was a baby, and it was sort of restored by Vril Dox getting Rann Zeta Beamed to its orbit, Maybe it would be better to say Tamaran has been lost to Starfire at times.
Barbara has some of Batman's control issues, though she lightened up from the early days of Birds of Prey. Back then, she knew everything about Black Canary, but Dinah had no idea who this "Oracle" person getting her to risk her neck was, and Barbara was fairly threatening at times to Ted Kord when they were messaging each other without either really knowing who the other was. I think Barbara tends to be more reserved, where Starfire has historically been open with her emotions. If you're her friend, she tells you. If she loves you, she'll say so. If she hates you, you won't be unclear on that fact. Superman's probably not as open with his emotions as Kori, but he's certainly not as stingy as Bruce. He never made any secret of Jimmy Olsen being his best pal, or that he cared deeply for Lois Lane. It's interesting that his openness with his emotions is apparently a product of his adopted homeworld, while Kori's is from the world of her birth (I think Superman would have been fine expressing emotion if he'd grown up on Silver Age Krypton).
Following Scipio's circus/theater idea, Starfire could certainly fit in the circus. She's a what, 6 foot 6 inch tall woman who is bright orange, in a fairly scant, purple outfit, who has flames/energy trail from her hair when she flies. She's going to be noticed, and her powers are very showy. Flight (with the aforementioned flame trail), super-strength, energy blasts. If she's not the strongwoman at the circus, she's probably the fire-eater or someone to that effect.
I'm tempted to say Oracle is more a director than actor, given her preference to stay off-stage and give orders to others. But she does get on stage occasionally, and it's a big deal when it happens (if Oracle's in the field, or her headquarters is under attack, the reader knows things are serious). She isn't necessarily physically dramatic in the way the Bat is with his swoopy cape and vanishing into shadows, but she's a capable dramatic presence. Her ability to locate people, breach all their defenses, learn everything about them, then use what she's learned in the most effective way possible, all that can have great effect. Imagine you're some villain. You think you've escaped from your latest heist to your quiet hideaway, but when you check your hidden accounts online, they've been drained. Then you hear sirens. Then you realize someone gained control of your security measures, and used your own cameras to see when you got home and sicced the law on you. You can escape, but you have to leave everything behind, run blindly into the night, and the most you might have to go on is that avatar Oracle used. Some computerized image no one has been able to learn anything about, except now you know she can get to you anytime she wants. First she's going to make you squirm. That's pretty theatrical.
(I'm not sure how to square Barbara's time as Batgirl into this. She certainly still has the theatricality, , but like Robin, she's more bright and showy than the Bat. Then again, I'm not clear on whether she and Grayson were together while she was Batgirl prior to the relaunch. My feeling is no, but there was a Nightwing Annual Marc Andreyko wrote that I think suggested otherwise, so I'm confused on that point.)
Given the number of writers and the years involved, I'd be inclined to say coincidence, but I don't know. It lines up so well to me. I'd love to hear your thoughts, because anytime I start trying to draw conclusions from the histories of DC characters, I feel like I must be missing a lot.