Hmm... So Steam and/or Stardock advertised buy both at a discount, but in reality the customer can only have one or the other (at any given time). Interesting marketing.
It's annoying the way that Steam handles DLC, I agree.. If I ever didn't just play all games with all DLC active all of the time I'd probably complain, but I can never think of a reason not to have the DLC active on pretty much any game.. I'm sure 98% of people are just like me, so Steam doesn't get too many complaints about it..