I agree. It's the same way in PHX where the US and UA gates are on the same concourse. The RCC there has had so many US Club members wanting to get in that they've posted a paper sign on the glass doors saying "FOR US AIRWAYS CLUB MEMBERS TRAVELING ON A SAME DAY UNITED AIRLINES TICKET ONLY."

One way to get around the silly rule if you really want to use the club: Just buy the cheapest refundable ticket on a same-day United flight and refund it by phone once you get into the RCC. This also works if you need to get past security without flying.