The reason the drivers are not set up as push pull is because the drivers in the picture are tweeters... no low frequencies. I have seen this before in some speakers.
High frequencies are very directional, and putting a tweeter on the back of a cabinet provides more reflected high frequency sound in the listening room. This, some manufacturers say, leads to a more spatial soundstage.
God damn it Logitech! why don't you update your digital 5.1 sets!! you brought out the z5500 5400 and 5450 (wireless rears) and they are the most popular and awesome speakers ever! you got a base 5.1 home theater for $300AUD that would kick the shit out of the base $1000 to $1500AUD home theaters from the home entertainment companies. more power and more features (all the dvd formats decoded)! they were just awesome. and how do you respond to this popularity? you discontinue the 5400s and 5450s! and leave the same 5500s in the line for like 5000 years without update!
why don't you bring out an update to them? the only speakers of yours i've ever cared about. like maybe 7.1? with hdmi audio/decoding?? and av sync maybe?