Donde has leido eso¿? Segun las especificaciones oficiales, no, son identicas salvo por el conector opt fan extra, que en este caso es innecesario puesto que no se va a añdir un disipa de cpu con dos ventis.
http://www.gigabyte.com/products/product-page.aspx?pid=4516#sp
http://www.gigabyte.com/products/product-page.aspx?pid=4491#sp
HD3:
System voltage detection
CPU/System temperature detection
CPU/System fan speed detection
CPU overheating warning
CPU/System fan fail warning
CPU/System fan speed control
* Whether the fan speed control function is supported will depend on the cooler you install.
D3H:
System voltage detection
CPU/System temperature detection
CPU/CPU OPT/System fan speed detection
CPU/System overheating warning
CPU/CPU OPT/System fan fail warning
CPU/CPU OPT/System fan speed control
* Whether the fan speed control function is supported will depend on the cooler you install.
Y la controladora es la misma.