This is true, and while they aren't in SVS sized enclosures, the larger SC def tech towers are quite large, and still have a decent sized enclosure. The only def tech towers I have heard with the built in subs were the older BP2004, not sure if it's the TL line or not, but for the room it was in, it sounded pretty good, but it definitely doesn't hit the lows like my svs does... but then again it's not designed for that. So while I agree, it's always best to have a dedicated sub, I still say that it's not always needed, it all comes down to your budget, room layout, and personal preference.