Thanks for pointing that out! For those interested...
"When you are waitlisted for a flight on Singapore Airlines, SilkAir or Star Alliance partner airlines, you will be given priority should a seat become available. This privilege is not applicable to award tickets and flights upgrades, or on flights where the waitlist may be closed.
This privilege extends to your immediate family members (spouse and children) if they are travelling with you on the same flight operated by Singapore Airlines or SilkAir."
It does appear to be applicable for non-Solitaire but only when traveling on the same flight.