Hi Aaron C,
Thank you for getting back to me and providing the additional info.
First, the problem with combining JS (and CSS) resources is that on each page the set of resources to combine differs, i.e. is unique, in most of the cases. So they must be combined dynamically in order to always combine the required minimum. Otherwise, one would have to combine *all* resources in one file so that all cases are covered. The downside of this is that the size of such a file will be very large and not optimal.
Second, when requested from CDN resources come separately, again for the same reason as above - there is no way for us to know each possible combination of resources that will ever be requested and provide combined resources for each case.
Third, we have some solutions in mind. One would allow you to specif some of the resources to be excluded from combining. This will allow the browser to cache these resources and later load only them from cache when required.
The second solution is to provide ways of combining resources in groups. For instance you may choose to combine the RadComboBox scripts into one separate file, so that this file is cached and reused across pages.
So I hope I have given you a better idea of how and why RadScriptManager works in this way and what are our plans of improving it.
the Telerik team