The link-level protocol of the USB is a very different one as the RS232. It uses 2 data wires, it is packet-based, it is master-slave and it can connect many nodes on a single wire (RS232 is bidirectional). The abbreviation of "universal serial bus" is a little bit misleading: it is designed to be so universal as the RS232 was, but it is not a stream protocol.
To have a direct stream connection between two machines, some type of data stream should exist over the link-level USB protocol.
The result is that in essence you have an usb-to-serial converter, which acts as an intermediary layer between the USB and a bidirectional data stream. It shouldn't be rs232, and also it shouldn't do a physical conversion.
You can buy a simple usb link cable to interconnect two machines. As two usb slaves can't be connected directly, they also need some intermediary usb master. This works mostly by giving an usb-ethernet interface to the machines connected with them, but giving an usb-serial interface would be possible too, and these devices may exist.
Next to the RS232, the Apple has developed a hardware-extended solution named lightning for that, although I would suggest more the RS232 direction on practical reasons.
However, there is a much smaller diversity in the machines bioses of most PC architectures. If you want a console redirection with them, you have only a physical RS232 connector on the mainboard for the task. Most BIOSes/EFIs won't even use an usb-to-rs232 connector, only the physical rs232 port on the motherboard.
