I could just as easily argue the opposite: If your operations can't handle individual system reboots you are doing it wrong. Rebooting and even rebuilding entire systems are not bad things in my book. In any case saying that this needs to be dealt with solely at the OS layer does not make sense to me.

Having said that, is is nice to be able to fully update an OS, including kernel, whilst running, but ultimately it is just a matter of abstraction levels and marketing.