It is unlikely that developers will have a better understanding of the requirements than testers, partly because testers work closely with the user community (and may be drawn from it) and partly because developers seldom work with the complete set of requirements in a medium to large development.
Testers may raise incidents related to the difference between user expectations and the specification, but these are not unnecessary. Such issues are more likely to arise at the later stages of testing.
Early testing (unit testing) is usually done most effectively by developers with a good understanding of the code and the development environment; they can be more efficient and more effective at this level. Later independent stages of testing offset any disadvantage from the lack of independence at unit testing level.