As you already stated, testers (normally) don't have the power, budget or other means to actually improve the quality themselves (as in rewrite code, extend deadlines, reduce features).
It can be argued, that by giving information to the decision makers (stakeholders) we do improve quality indirectly (if the people listen to our advice and act upon it).
By putting the decision not on our shoulders (or ours alone), one can share the responsibility and create a commitment for all parties involved.
Thats what I did in my current company.
A) It takes the heat and blame of the testers and my team.
B) I created a team for the release decision making of product management, developers and testers.
C) The collegues involved get a better insight, what is he current state of the product.
D) If they still need to release it (market, special feature, etc.), they decide so better informed and conscious.
E) By involving different aspects for the decision (market view, technical view, user view, aka product management, developers and testers) we made sure, that we cover all important aspects which should be seen.