Much information about Medicare on websites or in the media is oversimplified, out-of-date, or biased for business reasons.

Advantage plans are more profitable for insurers -- thus the heavy advertising for Advantage and none for Medigap.

The fact that Medigap plans are available is often hidden. Sutter/PAMF's "Your Health Insurance Information Guide" only covers Advantage. The loss-of-coverage letter from UnitedHealthcare -- notifying you that you will no longer have an HPInc or HPE group plan -- invites you to buy a UHC Advantage plan, but doesn't mention UHC's Medigap plans.

Many health insurance websites carry authoritative-sounding information -- and appear to be operated by government, non-profit, or other impartial sources -- but are actually collecting sales leads. (Including the official-looking "medicare -dot- com" and -dot- org sites.) 

For example, Consumer Reports and AARP are promoting "Chapter" -- a "free, unbiased Medicare advisory service" -- that turns out to be an insurance sales agency paying nonprofits for sales leads. Mixed reviews online.