PodBoy makes an excellent point about theater speakers. Something that is equally important to consider is the application (EDIT: as pointed out by bestbang4thebuck) - a home theater is a very different environment from a commercial movie theater, with different design goals and acoustical issues. Horns tend to be more efficient (thus taking less power to drive), but I don't see any reason to find a horn design essential to good sound.

The only horn bookshelf I can think of is the HSU Research HB-1 - proof that horns can find a place in applications like this, but their novelty as a horn-loaded design just reinforces the fact that the absence of horns does not a bad home theater speaker make.