Now when Microsoft has been preaching interoperability gospels and collaborates with the WASP you would be forgiven for assuming that some of that attitude might reach those who develop Microsoft websites.
Opera's problem is one single curious and invalid tag: <xhtml xmlns="http://www.microsoft.com/MSCOM/MNP2/Schemas"> stuck in the middle of the code. This changes to a different XML namespace and makes Opera ignore the following LINK tag which references most of the prettifying styles.
Why? I don't know Opera's source code. Perhaps Opera tries to handle what it thinks is a compound document? Compound documents are the most exciting part of the XHTML promises. This page isn't a compound document though, and it isn't even XHTML, so Opera should strive to ignore any indications of the opposite.