I think the answer is somewhere in between. The particular speakers you have chosen are designed for lots of low end frequency response (down to 30 Hz), which makes them a good option in a system without any subwoofer. That's not to say performance isn't better with a subwoofer, because it is.
Assuming you're going to have a quality subwoofer though, I think you can do better dollar for dollar passing more of the non-directional sound to the subwoofer, and buying speakers that don't produce all the way down to 30 Hz, maybe 50 Hz or so, with room to cross over to the sub a little bit above this.
That doesn't put you in typical bookshelf territory, although larger stand mount speakers can do this. Lots of floor standing speakers have that type of frequency response too. Your speakers just happen to really deliver the bass goods.
Any individual driver can only span so much frequency range. So it becomes a question of what drivers will best span that whole range. By default you've got a tweeter, then a mid-bass which could be anywhere from ~5.5"-10". The bigger your subwoofer driver, the bigger you'll need your mid-bass driver to be to get proper integration. Considering your sub has 15" drivers (I think), you're probably benefiting from the large floor standers. If you had say a 12" sub, I think you would be better off with smaller main speakers.