Here's an article about the Carter family and XERA:
Guest blogger Ed Hagen explores The Carter Family's time at XERA radio station in Del Rio, Texas in the 1930s.
birthplaceofcountrymusic.org
KWKH in Shreveport had the same power and central location as WSM. WLW Cincinnati had a country show. So did WWVA in Wheeling.
The other thing to know is that format radio as we know it didn't exist before the 50s. So WSM only played country music at night and during the Opry. The rest of the time, they were a variety station that carried the NBC network most of the time. As recently as the 70s, WSM was a full service MOR station by day, and country at night.
What really differentiates WSM from a lot of others is that it still sounds a lot like it did. It still runs the Opry (although the Opry is now a 5 day a week show instead of just Saturday nights). The station is basically owned by the Opry, and the studio is now located outside the front door of the Opry House. There's just a great connection between radio and music.