The great thing about a serial console is that it doesn't take long to figure it out. And you only need 3 wires to get there.
Another nice thing about it is that it's point-to-point, so you don't have to worry about your signals getting lost.
Heck, you can create a serial interface from discrete components if you're really into fun.
Wow. Miss the point completely. In the datacentre, trying to configure my SAN, I don't give a flying rats about whether my cable only needs 3 conductors and I can build a device using only discrete components. I'm not building devices and the cable came in the box with the device. I want to plug my special magical cable somewhere into a special magical and standard port somewhere on my laptop (ie, not a serial port), and have it talk to a special magical port somewhere on my device. I'd rather it be error detected and corrected just so that when partitioning my device, it didn't interpret "create new partition" as "wipe all partitions".
I strongly suspect a pl2302 or similar usb-serial chip that has linux drivers only costs a few cents, and the USB communications are error corrected (and the signal lines from the converter chip to the internals are all done within the metal enclosure of the device I'm configuring, so should be fairly resistant to errors). So if these devices were built included as standard instead, I'd have a much better chance of getting my data onto the device error free for some time in to the future until USB has been superseded. I've got devices at work that were advertised as containing "USB interface", which instead came with USB serial converters. They work fine. Just add udev rules to match the device and create a symlink somewhere in /dev, then configure minicom to talk to that location.
Of course, I'd be equally happy with ethernet (unencrypted telnet talking on some random private IP would be fine, this port need not be plugged into the network) - I'd configure my laptop to send all private subnet ranges to the ethernet port that was plugged directly into my device (if the laptop needed network access, have a second port or wireless).