Oracle, after all, has its own Linux ambitions. And remember this: Dell is Oracle's biggest reseller. Yes, Dell.
Let's examine that for a minute. Dell's Oracle server sales involve Red Hat Linux running Oracle or Windows Server sales running Oracle (with some Novell SuSE Linux running Oracle mixed in, I think). Dell already supports Ubuntu on the desktop, but has no near-term plans to support Ubuntu on the server. The moment that changes (it will, but it's going to take time), Oracle will most certainly follow Dell into the Ubuntu server space.
Meanwhile, SAP is doing extensive work with Novell in the Linux market. But Linux remains mostly a niche for SAP. And frankly, I doubt many Ubuntu customers really want SAP support right now.
So to say that SAP and Oracle are "holding out" on Ubuntu is just plain wrong. They're not holding out. They just don't see demand for Ubuntu Server Edition support -- yet.
Instead, Ubuntu server deployments typically involve LAMP and a growing list of open source server applications (OpenBravo certainly comes to mind).
Short term, Canonical really doesn't need Oracle or SAP to back Ubuntu Server edition. But long term -- say two years from now -- when Ubuntu has some serious server momentum, Oracle and SAP will be compelled to join the Canonical party. You can quote me on that.