It is not stated in STONE that a satellite radio antenna should go outside, but as a veteran professional installer I can tell you from real-world experience that it minimizes customer come-backs due to reception complaints. I have done probably 500 cars of all types with XM and Sirius and have gotten a feel for what will work reliably and consistently.
And if you read the professional training materials from industry groups, such as MERA, SAE, IASCA and manufacturer guidelines they all concur with my assessment. For a do-it-yourselfer an interior installation might be fine where you live, I am not disputing that. I have a lot of urban dwellers (Boston) who have found otherwise. Thanks and enjoy your smart!