Why cut reimbursement rates to cardiologists and oncologists?

I'm all for incentives to increase the number of doctors, especially general practitioners. 

But I don't know why the Administration proposes to cut the prices paid for cardiologists and oncologists by 11% and 19% respectively so they can pay general practitioners more.

Obama's War on Specialists

this boost for GPs comes at the expense of certain specialties. The 2010 rules, which will be finalized next month, visit an 11% overall cut on cardiology and 19% on radiation oncology. They're targets only because of cost: Two-thirds of morbidity or mortality among Medicare patients owes to cancer or heart disease.
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The way Medicare works is that Congress decides each year how much it wants to spend on doctors, period. If one area of medicine receives a larger slice of this pie, another must accept a smaller one.
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Jack Lewin, who heads the American College of Cardiology, said in an interview that the crackdown will cause "a horrible disruption" that will force many community and independent practices to close their doors, lay off staff or make senior patients wait days or weeks for tests and services.
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HHS justified its decision with a flimsy survey whose data it won't release and whose results can't be replicated. Dr. Lewin told us that both HHS Secretary Kathleen Sebelius and budget director Peter Orszag refuse to meet with him to discuss the topic.

Why heart disease and cancer, the biggest killers as people grow older?

Especially on top of a $500 billion cut in Medicare spending in the proposed health care bills.

Will seniors and boomers who are about to swell the senior ranks and so required to use Medicare stand for this?