Obama's Pander to Seniors on Social Security

The AP reports on Obama:

Obama said McCain would push to raise the retirement age for collecting Social Security benefits or trim annual cost-of-living increases. Obama has rejected both ideas as solutions to the funding crisis projected for Social Security in favor of making higher-income workers pay more into the system.

It's not clear why Obama wants Warren Buffett to pay higher Social Security taxes but not cut Buffett's benefits.