It's a business. And it wouldn't be blackmail by handing Batman to someone else. It's done all the time. "Do what we want, or we'll fire you and get someone else." Writers, directors, etc. are thrown off projects all the time due to getting into conflicts with a studio. It's the question of what he'd do when faced with that. Everyone in a creative field knows if they don't comply somebody else could swoop in to do their job. It's part of the glass floor everyone creative is standing on. Comply and aid to the best of his ability or walk. It is something that does come up a lot. And seeing as to how I think he cares about his vision of Batman, to him it would just be protecting it.
For example, I'm a writer. I know I don't have anywhere near a reputation. However. Studios hand me notes on a script and say, "we want this, this, and that." They are basic general notes that give me area to move around in. If I say no, they'd kick me off and bring someone else in. And my script, something I've been working a long time on, would be out of range and unprotected. Therefore, I'd be willing to compromise and work with them so I can secure it's safety and safe harbor. Middle grounds isn't a good place to be, but it is better than the alternative. Sometimes to secure the safety of your 'child' you have to make compromises because there's a real need to protect it. Basically they just know what strings to pull. Some comply to protect, others just walk away or get canned due to non-compliance.
I'm unsure how the heads of WB are. However none of the CEOs at various companies (in and outside of WB) have the reputation for being "easy-going" they got where they are for a reason. Sure there are some easy-going CEOs, or would like to hope so, but I've yet to meet one or hear of one from my own experiences and those of the people I know. It does seem like that element of 'old' Hollywood still exists, but you get used to it. I should probably note the executives and VPs I've run across have been more than easy-going though, so it seems just from experiences and what I've heard to be CEOs which makes me question if it's the same for the various studio heads around Hollywood or better.
Everyone at all levels in Hollywood faces this and yeah, you could call it blackmail. Not quite the definition of it, but it is a real threat though. It's also why in so many interviews everyone says, "yeah, I'm always afraid they'll find somebody else" or "that I'll be replaced one day." It's just part of the reason why being anywhere in the business - especially from a creative standpoint - isn't a stable place to be.
One example of the seediness of Hollywood is you know some of those crappy films Hollywood puts out per year? The executives and vice presidents don't even respect those films and see them as trash. It's just to meet a quota. Nothing more. Nothing less. I can't remember any particular examples, but actors have been forced into participating in films due to an obligation in their contracts with a given studio. The general audience doesn't hear about this. Everyone is on the same page whether the filming experience was brilliant or a nightmare. If a nightmare, people will hardly find out. Hell, I'm still getting used to the notion of putting out films a company thinks is bad just to fulfill a contract but it's done all the time. Actors, no matter how much the casting agency likes them, may even get thrown aside due to sexual preference. That's happened once on a superhero movie for a given superhero that I overhead the casting for. Talking mega-huge level superhero character. Basically - there's a lot of grey involved lol. You get used to it. There are just as many awesome people, scenarios, and stories about people as there are nightmares and you guys never really hear the full story most of the time whether it's good or bad. Basically, from all the Hollywood 'horror stories' even Nolan getting "with us or against us" treatment from the heads of WB if they see gold ahead wouldn't surprise me. Sometimes, and what the creative side has to 'deal' / live with, is it's all about the money for the business people.
One example, since it's what I've heard but I don't have any affiliation so I feel safe sharing is, you know Ben Stiller? That guy has one of the worst reputations in Hollywood. In interviews he seems like a good guy, people seem to say great stuff about him, he comes off great. However, behind the scenes? Really a nightmare to deal with and has had conflicts with those he's worked with. Even RDJ, on the set of 'Tropic Thunder,' stood up to him for the crew and everyone basically applauded him for it; so there's one example of a really awesome and down-to-earth guy, RDJ isn't just a great actor but he has an awesome reputation around Hollywood as well. So if there is a problem - that stuff never gets printed about or said in interviews for GA.