I've used Raspberry Pis since the first model came out and other SBCs and the lack of RTC has never really been an issue. The Pi syncs time by the time it makes it to the desktop. I can see it being useful for early boot timestamps but the most useful such log (dmesg) is just elapsed time since power on anyways. I can also see it being useful for devices doing data logging without Internet or regular power supply like a remote sensor logging device. I guess I just don't see it as a crucial component of a home router. I agree it's a cheap and useful addition though, just not maybe the most essential of one.