Onboard audio generally sucks. Why spend so much on a CPU just to waste CPU cycles on soft audio?
Secondly, Asus breaks more of Alex' Cardinal Rules of Motherboard Manufacturing. Specifically, it puts devices on the PCI bus that duplicate the functionality of the southbridge controllers. More specifically, instead of using a PHY to implement the other two SATA ports that the VT8237 supports, the Asus puts a Promise PCI controller on the board. Instead of the built-in VT8237 LAN, a PCI Gigabit Ethernet controller is used.
You only have 133 megs per second (theoretically) of bandwidth on the PCI bus. Via does not have the most efficient implementation of a PCI bus, either. So, 2x SATA = 300 megabytes/sec. 2x Firewire = 80mb/sec. Full-duplex gigabit ethernet = 250megabytes/sec. 630 megabytes per second of potential load on the PCI bus BEFORE any peripherals are installed. Picture trying to suck eggs through a garden hose.
The MSI has all 4 SATA ports powered by the NF3-250 chip, as is the LAN. Your PCI bus is free to handle video capture, firewire, sound (Get a nice sound card, you won't regret it) and anything else you decide to stick in the white slots.
The MSI, in my opinion, deserves our business in an effort to get the manufacturers to keep their hands off our PCI bus.