1. Because devices are doing new things and often by companies without strong software cultures that build in update mechanisms and look after old devices, so they are not updated as well as major platforms.
2. For some devices, you can't simply isolate them as full guests, because existing protocols from your phone allow LAN-to-LAN discovery and control, so special NAT-style routing into the DMZ would be ideal.
Related: the replacement cycle for devices like refrigerators, washer/dryers is not the 2 year cycle that we're used to for smartphone platforms. (e.g., even if your Android 2.2 phone can't be updated, you have probably replaced it by now.)
