I think there's solid business sense in keeping Nightwing on the shelves in a smaller DC lineup, but there's also Didio's/management's bias and that's been tripping us up the last few years. And I could just be wrong about the business, too. I think if Didio could justify it, he'd cut the title. And I doubt his bosses in WB really give a damn what is on the shelf as long as the rights remain intact and money is made.
However, I just saw that they announced books for Lois Lane by Rucka *and* Jimmy Olsen by Fraction (set for June releases, I think?). So as far as Im concerned that puts an end to the rumor of a 22 title lineup. No way does Jimmy get a solo title in a field that small.