Those other devices are progressive, getting annual updates which is completely different to a whole new generation of console hardware separated by 6/7/8 years and multiple hardware paradigm shifts. As long as consoles release with huge gaps and technology changes, BC will be a cost consideration. The logical change is towards a software abstracted platform, as discussed in the "upgradeable console" thread (or a shift to streamed gaming), which is a different concept and discussion to BC in a conventional console. As long as consoles are separated by such large gaps, the cost of BC is very high and generally not worth the cost. One can point to Wii and the ridiculous performance sacrifice made supporting BC instead of adopting contemporary, incompatible hardware.
It's worth noting that consoles (and 8/16 bit computers) have always been in a fairly unique position regards backwards compatibility. Display devices, satellite receivers, and storage have tended to have such slow transitions between paradigm shifts that they are mostly progressive (although we still have sudden changes without BC, like digital receivers and SATA HDDs, and even cars with unleaded petrol and catalytic convertors). The 8 bit era was the worst for devices being incompatible, which is part of the reason why PCs won out, because they offered consistency among other things. Modern tech like phones, tablets, and book readers are firstly too new to really suffer from hardware paradigm shifts requiring incompatibility, and secondly have started from a strong enough technology to support abstraction without crippling the hardware too much, thanks in part to an understanding of OSes that allow a lower impact by abstraction. But we still have plenty of BC issues. It's not like all Android apps run on all devices, and I can upgrade my phone and find apps that no longer work. Same with PC, actually.
