Edit: In rereading I missed your point on "racially inspired firing liability" and I concur with that as well. Especially in a time when one can get sued for spilling hot coffee on themselves.
I concur and can even example it. Back in the day, when I started working, you had a well defined set of 'jobs' even in small businesses - you had your secretary, you had your receptionist, you had your accountant, you had your manager, you had your assistant manager. Today you often don't even have an assistant manager at all in a smaller business, often times your secretary is a receptionist and even bookkeeper. And the manager usually has to be able to perform ALL those jobs so they can fill in for hours that the secretary is off (where as in the past they'd try to hire a second person, even if part time.)
I disagree that the 'hiring risk' is limited to minorities. If anyone has a flaw on their record, it is often not worth a businesses time to train them; a short employment term with another place, getting fired from a job, something on their background check, a poor credit report in some jobs, or even the innocent misuse of wording on a resume/poorly formatted resume. They say that the average time a resume is viewed is 30 seconds; you have to be affluent enough to make them want to pick you in that time or your resume is getting passed over. That is generally not a skill that low skilled workers have picked up yet, regardless of race.
Combine all of the above with a tight job economy and you end up with skilled people competing for low skill entry-level jobs, and obviously the businesses are going to hire the skilled prospective over the 'unknown' prospective.