Do they really mean "in all areas" and "will continue to be accepted until..." in Computer Science faculty opening ads in the US?
As to the research area, whether they really mean that any research area will be considered is impossible to know from the ad.  Sometimes the search committee really is open to a broad range of areas; other times, there is really so strong a preference for one particular area that people from outside area have essentially no chance.  I have served on search committees of both types; although the relevant verbiage in the ad was the same in either case, in one case, a majority of the committee was committed to hiring somebody from a very narrow area.

As to the deadline statement, I think that is pretty much always meant seriously.  The statements is there so that the committee does not have any possible obligation to not consider applications that are not completed until after the deadline.  There's no practical reason for the committee not to consider applications that come in a little late, and in my experience, slightly late applications have always been given full consideration.

By "slightly late," I mean a couple weeks. Actual review of the applications by the committee typically doesn't start until that long after the due date. (That's particularly true if the due date is early, falling during the winter break or earlier.) The latest application that I can recall getting full consideration was completed about a month late, but at that point things are probably getting dicey. And (just like in graduate admissions) committee members are likely to be more flexible about the dates of recommendation letters than the package put together by the job applicant.