An important aspect of XBAP
performance is its start time. If an XBAP is the first WPF application to load,
the cold start time can be ten seconds or more. This is because the
progress page is rendered by WPF, and both the CLR and WPF must be cold-started
to display it.
Starting in .NET Framework 3.5 SP1, XBAP cold-start time is
mitigated by displaying an unmanaged progress page early in the deployment
cycle. The progress page appears almost immediately after the application is
started, because it is displayed by native hosting code and rendered in HTML.
In addition, improved concurrency of the ClickOnce download
sequence improves the start time by up to ten percent. After ClickOnce
downloads and validates manifests, the application download starts, and the
progress bar begins to update.
So XAML Browser Applications or XBAPs are designed for web
based applications which will require .NET Framework 3.0 or later in end user's
machine. Whereas WPF doesn't require the framework and its totally a windows
application. Silverlight is completely for web based applications when you are
targeting a number of platforms and browsers. But one common thing in all these
three technologies is XAML, which is required to design the markup.