The 5.2 would require a sub if you are expecting that Home Theater LF experience. But remember you can have a very satisfying HT experience with a PC and the $59 Creative Labs 5.1 computer speakers...its all relative.
The 5.2s could certainly be used, and I'm sure are used, for music without a sub. This would be for people who do not play a lot of frequencies below 48Hz. The lowest notes on the piano, pipe organ, and double bass go below 48Hz. Also 48Hz may be lower than any speakers you have heard at a louder volume.
But they won't faithfully reproduce the lower bass, such as pipe organ or more likely, synthetic/techno music that is more common today. For that you would need a sub(s).
Not to say that you would not be very happy with them in a small home theater environment. It depends on how extreme you want to go, what your lifestyle is. You can damage your hearing watching Action DVDs at loud volumes! You can also damage the structure of your house with low frequency! On the other extreme you can miss those LOW notes you may want to hear at reasonable volumes.
To me the Teak Prism 5.2s are amazing values for the money if you want decent speakers, beautiful speakers, and unique objets d'art in your home. And they are better than MANY speaskers out there in that price range. The value of the Teak wood, drivers, and the labor make these speakers a steal. But you can only have one L and R speakere, so get the ones that best fit your lifestyle. If I had FOUR sets of speakers, I would have these in a heartbeat (I have 2 sets of Marble 9.0s and one set of Teak 3.0 Prisms). If they are calling you , get them!