Some of that is leftover from the days where they were different companies. There are still aftermarket radios being sold from those days.
The PAD information (what displays on the screen for radios that have a screen) on modern OEM car entertainment systems, display SXM, because that's the logos that SXM are sending to the receivers.
Yesterday while driving around, I noted that the PAD logos on my XM radio screen looked older or different. I suspect that's because they were running on either their backup automation system, or something happened to specifically the PAD, forcing it to be displayed by their old Harris DAL automation. Glitches with their PAD display seem to be a weekly occurrence, which usually gets straightened out within 24 hours.
The fact is that SXM still have three different delivery methods: 1) The original type of geosynchronous satellites used by Sirius. 2) The original type of geostationary satellite(s) used by XM. 3) Internet Streaming.