Mark Baumann, a 44-year-old uninsured diabetic, sees in the Obama administration's health-care law a future with stable coverage to pay for his insulin shots and blood tests. That's likely to come indirectly at the expense of his mother's generous health-care plan. Humana Inc., Mary Baumann's insurer, intends to pare her "Medicare Advantage" plan to make up for the smaller government payments it will soon receive as a result of the new law, leaving her with higher costs or fewer services. On the table are beefed-up co-payments and premiums, as well as the loss of perks such as her free membership...