In my experience, many HTiB's with "wireless" rear speakers are not truly wireless; they have a module that requires a power outlet, and the rear speakers plug into the module. True, you won't have speaker wire running from the front of the room to the rear, but you'll have it going side-to-side instead.
I'm sure most members here will suggest running speaker wire if and whenever possible to ensure highest quality sound.
I would guess that the recent popularity of soundbars have replaced the need for HTiB with wireless rear speakers.
Panasonic TH-42PE7U plasma, Toshiba HD-D3, PS3, Shaw DCX3400, Yamaha HTR-6160, Polk 6.1, Belkin PF30, Harmony 700