fathom - 6:51 am on Apr 16, 2012 (gmt 0)
I don't see anything that would lead me to this conclusion Sgt Kickaxe.
My best hypothesis here would be that they handle anchor text differently
If you have a diverse link anchor text profile... you don't see any depreciation in the anchors' value.
If your profile is predominantly a few different phrases... that's a red flag for unnatural.