Line-out guarantees that even if there's DRM in the streaming decoder, you're getting the actual audio stripped of all DRM.

It has the simple elegance of writing your DRM protected audio to a CD and then ripping that to MP3, which is a process most non-audio nerds already understand from the DRM iTunes days.

That said, I agree that you could get a slightly more accurate sound with a virtual audio pipe than if you use a DAC/ADC combo, even if modern jitter is negligible