Having a cover letter is an extra, your resume is the center piece. You can have a resume without a cover letter, but you can't have a cover letter without a resume. Not including a cover letter helps me to get in the door, if a potential employer is serious about hiring me, I have no problems preparing or giving them past writing samples. I am an individual , and I'm not bound by EEOE rules, that's another reason I can disregard time honored industry practices, and how its a bigger deal if a company ignores resumes.
on right because...
its the first sign of arrogance and disregard to throw away the intellectual capital of time honored industry practice
cover letter is industry standard too, yo, but you disregarded it