Correct, Dan. The Base-USA template uses advforecast2.php (either the older V4 or the ‘beta’ V5 script) which depends on the NWS for data.
Likewise, the Base-Canada template uses ec-forecast.php for forecast data from Environment Canada.
No changes to DarkSky are needed for either USA or Canada users.
Only the Base-World template used WU-forecast.php and must switch to using DS-forecast.php for DarkSky before 15-Feb-2019 when the WU API is planned to be shutdown. The same applies to any standalone user of WU-forecast (switch to DS-forecast.php).