Generally the "must have X shipped titles" requirement on jobs postings is just to scare off the noobs. If you have awesome art, you don't really NEED that experience, but it helps.
Its all about showing relevant skills though, as is the case with any resume in and job field, experience on lower spec games will make you more attractive to a company that does similar games. If you're applying to a studio that does high end games and you only have low spec titles on your resume and low spec art in your portfolio, you're certainly at a disadvantage. However, having *some* work experience is always better than none.