It's not a matter of "excuse not to read" extensions. The Extensions are vendor specific. This enables a vendor to provide additional levels of detail within any GPX data type (Waypoint, Track, Route). Companies create their own GPX schema for defining Extensions; some of that code may be binary - as in the case shown in my "B" section above labeled <gpxx:Subclass>. Although it is required that vendors publish GPX Schema, they do not have to offer up their Nav Engine code to others. I should also add, that since a vendor's GPX Schema is published online, other vendors can choose to read/write those extensions: minus the binaries of course. For example, FURKOT.com will Export Waypoint data like Address/Phone# in GPX Garmin Extensions.