Frankly, I'm amazed how far people can get without learning the basics of citation styles. I've edited many Master's theses and even a few PhD dissertations in which key parts of citations were done incorrectly. These things should be mastered in first year college.
Let's review the purpose of citation. We use citations to provide credibility to the arguments we are making. A citation answers the question "How do you know?" for each fact that you assert.
APA style uses two criteria to show how much weight a source has: author and date. It assumes that later citations are more likely to be correct than earlier citations. It also assumes that some authors are more credible than others.
But APA doesn't want you to fill up your page with a lot of other junk that's not necessary to show the credibility of your source. That's why the URL and publisher information are listed in the reference section. The whole idea is to keep the body of the paper nice and tight, and leave it up to the reader to check out the reference section if he/she wants more information or to track down the original source.
I just finished editing a Master's thesis in which almost all of the in-text citations did not appear in the reference list. In the reference list was a whole bunch of stuff that was not cited in the paper. It's a complete disaster from a credibility point of view. The reference list is not suggested extra reading for anyone with a burning interest in the topic. The point of a thesis is to make an argument and to show that the facts behind your argument are credible. References should be strictly a list of sources of information actually used in the paper.
Don't Master's programs require you to write a number of essays in courses leading up to your thesis? I know that some undergraduate teachers can be lazy or inconsistent in checking writing for APA style, but surely there must be some kind of course for people who are required to write a thesis? I'm actually shocked at some of the people working in graduate-level programs. I think (private universities are particularly guilty of this) that the admissions offices looks at the tuition fees more than the academic ability.
I think part of the problem is the move to teach undergraduate courses by sessional instructors. These instructors are underpaid and over-worked. They may not have the luxury of time to carefully critique papers, thus teaching undergraduates how to write proper academic essays. When I was early in my education, I thought references were for the birds. I was casual about citing sources. A great teacher set me straight. After that I was diligent in citing sources, but rarely did I get a paper back where a teacher had corrected some technical aspect of my citations. Really, it took until I became a professional editor that I learned about sources like Purdue's OWL, which sets out clearly all the formatting to properly reference a paper in MLA or APA style as well as providing other writing instruction.
If you are an undergraduate and you intend to go to graduate school, or continue your academic career in any way, you need to ensure you understand how to use citation styles properly. Access your school's writing resources, or take the time to look things up online. Even if your mark doesn't depend on it now, it may be important later. And it could be too late then.