They don't apply it to the html5 stream. I periodically write in and complain about DRM to them. I really suggest others do too, to highlight the issue. I also don't like the fact that the Sounds app contains a ton of trackers as well as DRM, and I've highlighted that to them as well. I usually get a sympathetic, if ultimately futile, response.
The BBC buys in very little, all told, and I suspect they will move to Widevine at some point.