Actually the heatsink assembly is not any better. The ASUS board additionally has fully sealed higher performing inductors ( chokes ) vs the Extreme 4 which looks like they are fully sealed but are hollow inductors.
I will upload a pic for reference a little later.
There are number of additional factors the ASUS board has over the extreme 4
1. Superior Fan Controls ( all 4 pin headers with manual control for each header )
2. Superior USB 3 Performance with full UASP support
3. USB Charger + which allows for quick charging of non iOS devices ( smart phones and tablets ) compared to ASRock which is only iOS
4.USB Bios Flash Back - A great option for low level direct UEFI flashing ( no cpu, memory or graphics card required just the PSU connection ) this is great in the possibility the chip corrupts whcih can occur potentially during surges, spikes and brownouts. You can recover the rom even the system does not post.
5. Higher quality components.
Fully sealed inductor ( chokes ), 5K capacitors ( twice the lifespan of ASRock "gold 2K" capacitors ).
6. Superior UEFI with full .CAP support ensuring the best interoprability, compatibility and performance for Windows 8 but Windows 7 users also benefit
7. The PCB is a thicker PCB which has superior rigidity which is need especially if using backplate based cooler which can placed alot of stress on the PCB
There is even more but overall the LE PLUS is a very strong board when you fully consider all points of value. Especially when looking at functionality of the board.
Hopefully have provided some insight that ASUS boards can definately offer great bang for the buck and true value when carefully evaluated. Value does not mean low cost but regardless of the price is justified with there are plenty of 150 to 200 dollar boards that have a low value in many regards if you begin to look at all aspects of usability. Overall hope this has helped.