Some receivers have room response compensation for sub as well (SR6010/7010 for example) or you can use other products for that if you wish, but that is not necessary how ever. Most of companies try to market their products with many kinds of things. Genelec makes really good speakers and subs, but they are expensive when you compare them to competitors.
I see that SVS sub prices have gone up AGAIN for european market, that is a shame really. I myself was about to buy SVS SB13-Ultra but they raised the prices and I went with BK XXLS400 instead for less than half the price! My room is similar size to your and has huge windows on one side as well, I use curtains on windows when watching movies to help with reflections. So I'm pretty sure that XXLS400 or Monolith+ would do really nice job in your room as well. I'm only using about 1/4th of the power from my XXLS400 and it produces powerful and accurate bass in my room, have nothing to complain about that sub at all. Love it with both music and movies, sometimes it still surprises me while watching movies how well it performs. You may think that BK subs are cheap and can't compete with more expensive subs, you are fooled by the price as these guys can sell their subs for cheaper as they sell directly. If they used retailers their subs would cost a lot more. I myself went with XXLS400 for accuracy over the low extension and more power of Monolith+.