A variety of styles...

A number of...

These concepts are clearly plural in meaning if not in form. It's a question of whether we grammatize by form or meaning. A similar question might be raised about the choices the city expects ten inches or less of snow tomorrow or the city expects ten inches or fewer of snow tomorrow. If we went strictly by form the latter would be the correct version but we go by meaning (we're measuring snowfall not counting inches) making the former correct.