This is what MS said on the issue (from Wikipedia):
"With the release of IE6 Service Pack 1 in 2003, Microsoft announced that future upgrades to Internet Explorer would come only through future upgrades to Windows, stating that "further improvements to IE will require enhancements to the underlying OS."
I think Vista messed up their plan. It doesn't sound like they just thought they were done. At least that was what they said in 2003. Now maybe you're saying internally something else was happening, but I hadn't heard that before.
Apparently in 2005 they then announced that they needed to do an out of band release for security.
"With the release of IE6 Service Pack 1 in 2003, Microsoft announced that future upgrades to Internet Explorer would come only through future upgrades to Windows, stating that "further improvements to IE will require enhancements to the underlying OS."
I think Vista messed up their plan. It doesn't sound like they just thought they were done. At least that was what they said in 2003. Now maybe you're saying internally something else was happening, but I hadn't heard that before.
Apparently in 2005 they then announced that they needed to do an out of band release for security.