This is incorrect. You can quantitatively measure "quality", and all it takes is a little effort to define criteria. The easiest example I can think of is measuring the average amount of time required for users to complete a task. For things like web sites, this can be gathered trivially via Analytics or any other stat program. There is nothing subjective about it -- if you do it right. Most usability professionals know how.
As for programmers working alone, though, that's something no one else can solve.