Although the ISM band - the 2.4GHz used by most routers -- is divided up into channels they don't actually exist in a real sense because the modulation used by WiFi spreads across about a third of the band. (So you get three usable frequencies in the US, maybe four in Europe and Japan.) The problem you as an end user has with WiFi is that you don't get interference in a traditional sense, you just lose bandwidth, something you may not notice unless you're transferring files or streaming. Wireless networking shares the medium by slicing it up in time but the protocol isn't very efficient when the network gets congested, hence the collapse of throughput.
I tend to cheat at home. I put Cat5 cabling in years ago which runs our computers and high bandwidth entertainment devices, leaving wireless for less critical / more bursty applications. I'm not sure whether beam shaping or other technologies will have disguised the shortcomings of WiFi by now -- its the sort of thing that works well in the lab not not necessarily at home -- so the idea of having low power APs distributed around sounds like a decent solution provided they use a clean backhaul (cable, preferably) and not the store and forward repeater functionality built into the protocol.