If the firm is specified, then client may have written ad. But were you serious that you saw or read ads for attorneys with zero to three years experience requiring or desiring such requirements ?
I do know one specialty area which has a substantial number of openings nationwide which is open to those with zero experience in that practice area & just basic requirements, but few receive offers due to the years long training required. I guess that they are looking for a certain personality type in addition to bar membership & an interest in that practice area.