Yes, they are still available. The SPI master mode is implemented in hardware. Maximum SPI clock is 30 MHz in master mode.
For Windows you get this API:http://www.lcdinfo.com/usb13700/documen ... 00_8h.html
The SPI is included in the ExPort... functions. In the description there you will also find more detailed specifications of the SPI operation. There is currently no special touch panel support provided.
It doesn't need constant data stream to update the display. Only when the image changes. Also it is possible to only send the areas that have changed and you don't need to refresh the full screen if you don't want to. As it's monochrome the data amount can remain quite small if you don't need to refresh very often.
One example of Linux support is the serdislib library:http://serdisplib.sourceforge.net/ser/usb_usb13700.html
USB13700 is also included in the lcd4linux compatibility list:http://ssl.bulix.org/projects/lcd4linux/wiki/Displays
Even if not specifically for Linux you may find the myLCD library useful:http://mylcd.sourceforge.net/libusb13700/index.html