With the ArcGIS Server JavaScript API, you can find the URLs in the map services in the source code. Do the Flex and Silverlight APIs completely obfuscate the map services URLs?
As an example, the County of Ventura has this web application in Flex. However, there doesn't seem to be a way to find the rest services URLs for the map services that one could use in their own applications/mashups. Perhaps obfuscation is the point to using a compiled web application vs the JavaScript API?