Yes, you absolutely could do that. That's the way you would have to do it to get the API to work to avoid having the browser pull the code from Esri's site. I don't know what's running js.arcgis.com but assume it's some massive high availability thing at Amazon Web Services. So in fact, for OUTSIDE customers, it's probably faster. For people ONSITE the page probably now loads a tiny bit slower. It's creating traffic on our Internet connection that was not there yesterday. What to do?
Given that when you pull up an app, it loads the API only on the first call, and sadly given that employees here are not ALL using amazing and wonderful web maps, it's a really probably wash.