Where do you have that from? Nvidia has both 9300M and 9400M on their website, for 9300M the core clocks are 400 (with 64-bit bus), for 9400M there is no clock info given but it has 128-bit bus.
You are confusing the discrete 9400 GS/GT GPU core (G96) with the motherboard chipset/IGP called 9300M/9400M G/9400M GS (MCP79).
The later have dual-channel (128bit) memory support for either DDR2 or DDR3 memory.