dedicated vs. book shelf

In a true home theater system, surround speakers only have to handle the frequency range of the surround sound track, which normally is limited in both the low and frequencies (typically, 10 kHz at the high end). A good book shelf speaker, however, will have frequency response ranging from around 60-80 Hz up to the 18-20 kHz range. Also, true surround speakers are built to distribute the sound more widely, so you will see both dipole and tripole designs that project the sound along the walls of the listening room. Obviously, a bookshelf speaker can be made to function as surround speakers, but their are not optimized for this purpose.

The Klipsch bookshelf will be more critical of placement, and would need to DEFINITELY either be aimed directly at the listeners ears (Horns are very beamy, with steep waterfall plot), or re-EQ'd for proper tonality from listening position(s). In most setup's, you'll be likely placing the rears near a wall/room boundary, which also requires EQ'ing the speaker (although this is handled much better now that room DSP correction is available), as bass modes will be excited and speaker/boundary boost will imcrease the bass, relative to the rest of the spectrum. Also, you'll need to place them high up, to make them not so localizeable, otherwise they'll draw too much attention away from the main soundstage.
In short, the K bookshelf will be a bit critical, and picky about placement, and less than optimum to cover a large seating arrangment.
On the plus side, that speaker will be very dynamic, have good detail and inteligebility for a properly located seating position, if set up correctly, EQ'd, etc. But, in my experience, it would be much much better suited as a surround in an audiophile setup with a smaller seating area, even single/dual seating setup.
The dedicated bipole/dipole Klipsch rear is first going to be designed to be located on/near a wall/boundary. They're also more difuse sounding for better surround coverage, and more forgiving of placement, while still maintaining intended tonality. You also hear more reflected sound, not direct sound, overall, which emmerses you in a sound field a bit better, IME. And yet, they still offer good dirrectivity in the bipoles as a point source, er compromise for music and movie mult-channel sources.
Overall, I find the Klipsch surrounds make more flexible, use-full surround speakers, regarless, in movie/music applications. I would usually default to these, myself. But, it does depend on variables, how well each balances with your system or lifestyle, and taste, and other.
In the end, you can do well with both, but they need to be adressed differently, and erquire much different approaches to integration and system needs.