No workie on my 2004 USDM STI, which is DBW, while the WRX is not. I didn't expect it to work...
Neverlies, exactly what model year, market (edm? usdm? jdm?), and model is your car?
I hooked everything up, hit the Read ECU button, turned the key to ON, then clicked OK on the dialog box for ECUflash. I tried about a dozen times.
Here's my flash setup and log files (ecuflash and portmon):
http://freon.shackspace.com/ecu%20and%2 ... /flash.jpg
http://freon.shackspace.com/ecu%20and%2 ... /error.log
http://freon.shackspace.com/ecu%20and%2 ... /flash.log
The portmon log looks ok to me. I just don't think the DBW STI ECU is as close to the cable throttle WRX as you are thinking. But if you have a DBW STI, then nevermind, maybe I'm screwing up.