WASHINGTON (AP) — It sounds like good news: Annual premiums for job-based family health plans went up only 4 percent this year.But hang on to your wallets. Premiums averaged $15,745, with employees paying more than $4,300 of that, a glaring reminder that the nation's problem of unaffordable medical care is anything but solved.The annual employer survey released Tuesday by two major research groups also highlighted another disturbing trend: employees at companies with many low-wage workers pay more money for skimpier insurance than what their counterparts at upscale firms get.Overall, "it's historically a very moderate increase in premiums," said Drew Altman, …