I think SQ still own quite a large part of their fleet...
Since SQ have the resource to buy new jets every couple of years... They may well sell their older jets soon... And SQ tend to use newer jets to keep maintiance cost down which is 1 big reason of SQ have a very young fleet...
Since if the jet is still relatively young when SQ sell them, they could still be sold at a very good price... But wait a few more years when many other airlines would be replacing the type at the same time... It would be harder for SQ to sell their fleet and also earn less from it...
So it really wont surprise me to see some SQ older B772 leaving the fleet by 2010/2011...