Re: Airworthiness directives
I think the answer to that, Kolibear, is that it depends on the likelihood of the manufacturer getting sued big-time.
Example: In the Lycoming defective crankshaft saga, L paid for everything, including engine removal/refitting. I believe that they also paid, rather more quietly, for AOG costs incurred by commercial operators. This was done even on planes way out of warranty.
However, many other safety related issues are left to the owners to pay for. The manufacturer issues an SB, which typically does not become an AD. I can think of defective aileron joints in a particular type of aircraft; the SB was never made mandatory, which means it was optional, which enabled the manufacturer to wash their hands of paying for the work - even on planes within the warranty!
So there is a lot of politics involved here. The nearer the manufacturer gets to making something "not optional" the more likely he is to have to pay for the work, so the pressure is on to pretend it isn't important... Lycoming can't do that as easily anymore; the FAA is right on their back now.
In the software business, it is also possible to sneak in a fix for something quite serious, in the guise of a routine firmware update (for example in an autopilot) for an ostensible problem which is very benign. I've seen this happen.