The USB serial port is required in order to use the runonphone tool, and is also required to do a package install without first putting it on the memory card. Currently, you can enable the serial port manually, by specifying "vendor=0xXXXX product=0xXXXX" when loading the usbserial module. The IDs you can find by looking at the output from "lsusb -v".

The detection of these ports should be automatic, and probably has to be done upstream, either in the Linux kernel, or in the udev scripts.