It sounds like they have to actively block it to disallow it.
I don't think that's important. It's a feature that Sony introduced and just like custom soundtracks on the PS3, just like the screenshot function on the PS3, they give the developer / publisher the chance to simply not support it – I don't think it's important wether they have to actively do something or not.
The idea „let publisher decide“ is a huge problem of Sony this generation. It's the reason content on the PAL PSN gets delayed constantly, it's the reason why we don't have a lot of demos for PSN games, it's the reason some of PS3's features are nothing but laughable (custom soundtrack, video recording, screenshot feature) and I want Sony to finally acknoledge that what's good for the publisher isn't necessarily the best thing for your customers. Microsoft has very strict rules about everything but that's partly the reason why everything on the Xbox 360 seems to work so seemlessly.
That's what I said, plus spoilers can be subjective. What a developer considers a spoiler may not really be a spoiler. Even so, we can still take a picture with a camera if they disallow it.
Time to create a YouTube channel filled with videos of the parts of games publisher won't let you take you screenshots of.
![Big grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)