This was widely reported back in 2008. The ball started when US announced for their elites no more 500 mile minimums:
http://www.flyertalk.com/forum/us-ai...r-segment.html

UA then announced the same policy for UA elites (as well as earning minimums on other carriers).
http://www.flyertalk.com/forum/unite...ts-merged.html

However, UA changed their mind and granted 500 mile minimums for elites (but we didn't get back the 500 mile minimum on US)
http://www.flyertalk.com/forum/unite...ion-rules.html