This PDF from Forrester Research is a nice high-level description of the role and importance of XAML. Pass this on to your decision makers.

EXECUTIVE SUMMARY
Microsoft has unveiled a powerful weapon that will allow it to consolidate its control of the desktop by offering tools across development tasks and roles with high levels of integration. This innovation goes by the opaque acronym of XAML (eXtensible Application Markup Language), but don’t be fooled: The possibilities inherent in this technology will make it extremely important for enterprise developers, their tools, and their processes. This, in turn, will dramatically influence the attractiveness of Windows Presentation Foundation (WPF). And yet, XAML has been largely overlooked in the evaluation of the broader impact of Windows Vista and WPF.