Sounds like the real answer to this problem is an improved USB to serial dongle. If this is a serious problem for electronics engineers, they are the perfect people to fix it. Whatever the problem with the USB to serial interface is, fix it. Then sell your improved serial port adapter for $100. Profit!
The problem is not the hardware. It is the software stack in the middle which is necessary to implement USB.
If only there was a way to put, say, a 16550A chip on the processor data bus and hook it into the port I/O logic... (/sarcasm)
Actually, English is what the speak in Britain.
The local language is American.
I work in embedded software (tiny little systems, not something like embedded Linux).
Software systems for some of these chips dates back to Windows 3.1.
There is insufficient support for this software in Vista / Windows 7.
Not to mention direct hardware access to system resources like RS232 ports (USB COMM ports
need not apply).
365 Days of drinking Lo-Cal beer. = 1 Lite-year