Of course. Similarly, when you are submitting a PR to an open source project or a manuscript to an academic journal, it's your job as the author to take note of contributor guidelines.
Yes; Wikipedia's expectation is that authors have researched the topic about which they are writing, and therefore they are in the best position to provide the sources from which they got their information. The editors' job is to ensure that Wikipedia's standards are met, not to re-do the research that the author should already have performed.
If the case is that no research was performed because the author is already an expert in the area, they are still expected to provide citations so that the same standard can be applied to all authors.