It would be nice--but keep in mind that while your cover letter may be the last part of your application package you write, it's probably going to be the first thing the employer scans to see if you look like a good candidate.
Think of the cover letter as an abstract, or a précis--the same sort of thing you might have been asked to write as you develop a literary research paper. It's where you give a brief, succinct summary of what's inside the paper (or in this case, the application).
Here are some resources to help you construct a great cover letter:
Template, paragraph by paragraph:
Mistakes to avoid
Samples of cover letters, organized by what they contain