Jeff,
I am not familiar with that platform. I designed developments boards (A4 page size) with FPGA's and tons of interfaces/peripherals on it.
No, the problem with the USB to JTAG interface is the software interface. We did not see the need to spend the time (man hours) to design a USB JTAG cable and software.
I agree that working from a laptop is a pain, because there is no parallel port. Check out FTDI Chip, they have some simple USB-to-devices. I know they have a USB to parallel port chip, but it might be difficult to implement because I have heard that these type of chips don't emulate a LPT port but rather a printer... Now I have NOT looked into this so I can't say more than that, but I might be wrong...
Best regards
Sandi