For a lot of roles in a development team it is pretty obvious how these roles are invested in the quality of releases of their software. Developers who accidentally write bugs know that when the call comes they'll have to postpone what they are working on and get to fixing and quickly deploying something. Manager-types see their planning go down the drain and risk having to do damage control on escalated calls from angry customers. Because of this these people have some serious motivation in making sure the software is as problem-free as can be, aside from their general professionalism and attitude.
There is one category where I cannot easily come up with ways they are vested in the releases and that is the testers. There are examples of companies where code quality and bugfree releases suddenly became very important to developers when they themselves started to be on-call for nighttime and weekend support. I won't say they became more professional developers, but their attitude surely shifted because they started having a more vested interest.
But how are testers, aside from attitude towards their work, vested in the releases they test?
I'm not looking for a way to place blame on testers or developers and yes, I do realize that a professional attitude goes a long way but it is not THE way. Let's look at this another way: when somebody feels like throwing up, you can quickly grab a bag for them, or can just let them throw up on the floor and clean up afterwards. I'm pretty sure that everybody would go for a bag because it's just easier to not have to clean up. But when it's not you doing the cleaning, why should you care what happens?