erm, yeah
"But does it have the will to buy the last-standing privately held database vendor?"
You have completely omitted that EnterpriseDB sells its own version of Postgres and that its business has been doing very nicely since Sun borged MySQL and Oracle borked the Sun acquisition; the Oracle compatibility certainly helps. Netezza is another Postgres+ (in the sense of added value) vendor. For customers there is a lot of sense in keeping things the way they are which may be why Postgres has been making such great strides recently, 9.1 is really going to get a lot of interest.