Just because the manufacture sells it, does not mean that it is right. All speakers in your home theater should be the same as your left and right. Center speaker designs have evolved because of the aesthetic idea that they need to be oriented sideways or be physically smaller to look good above or below our TV's. Marketing and sales love this, because now you "need to buy this center channel speaker." It even looks different than anything you have. Oh, and the same goes for these surround speakers. You need some of these too. In the old days, this was true because the old di-poles were supposed to provide a diffused sound field from the Dolby Surround soundtracks. Now we have Dolby Digital 5.1/6.1, dts 5.1/7.1 etc... which requires multiple full range speakers that can image just like your front speakers. Why do manufactures still sell di-poles? For marketing of course.
As far as the mix goes, 50% for the center, 40% for the L&R combined and 10% for the surrounds. So the center channel needs to be equal to the L&R or the best speaker in the system and often it is not. Most horizontal designs have a narrow dispersion characteristic which is not what you want either. The Dolby digital frequency recording spec is 20-20K for all channels. So yes, your 40hz center channel is "light weight" or less than ideal. The sub channel is 3-120hz for special effects.
One thing to keep in mind about home theater vs. 2 channel. The goal in home theater is pretty good sound for the audience (multiple seating locations). In 2 channel we are going for the ultimate image "you are there" experience. Proper speaker choice and set-up can go along way when it comes to home theater. Five or six really good hi-fi speakers and a sub can kick ass on most manufactures "home theater systems."