No, it's not speculation - it's the way the law is written.
The definition of commercial use applies to the venue - not the DJ. A DJ playing at a club does not derive a commercial benefit directly from the music as does the venue who turns it into immediate cash sales of food and beverage. The DJs wages are not a direct benefit of the music they are a benefit of his labor. The wages of the waitstaff are also not a direct result of the music. The profit margin of the venue on the other hand, does derive a direct benefit from the music - and so that is where the law EXPRESSLY places the liability.
To understand this - note that if you take away the music (imagine the DJ as a game show host instead) nothing except the profit margin (turn out) changes. All of the wages expenses remain.
No DJ has ever been sued (and never will be) because the law's definition of commercial use does not attach to the DJ who performs within a third party venue.