Based on the checked baggage tool on United’s website, it appears they’ve changed the checked baggage policy for Star Alliance Gold members.
Previously Star Alliance Gold members could check up to three bags weighing up to 70 pounds each, as is still the policy for Premier Gold members and above.

However, suddenly the baggage tool shows that Star Alliance Gold members are only allowed one checked bag weighing up to 50 pounds on domestic itineraries.

So they’ve not only reduced the number of permitted checked bags for Star Alliance Gold members by two, but have also decreased the weight limit by 20 pounds.
Best I can tell there was no announcement, aside from this message posted at the top of the checked baggage tool:
We have revised some of our checked baggage policies for travel worldwide. For the latest checked baggage updates, please review all relevant baggage pages before you travel.
Updated: October 17, 2013
What can really be said, other than…

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