The difference in the recoil lugs is the length - how far they go down into the stock. The AccuStock can get away with a shorter lug because it's butting up against an aluminum skeleton. The standard lug (in factory stocks) is butting up against softer wood or plastic so the additional surface area is needed to disperse the energy w/o damaging those substrates.

For what it's worth, I've seen a few of the longer standard factory lugs from mid-size magnums (.300 WSM, .300 WM, .338 WM) that were bent from recoil. I've also see one of the factory lugs from a .338 Lapua Mag that was bent from recoil. The way I see it, spending the $30 or so for a quality aftermarket lug is just cheap insurance if you're shooting high energy cartridges.