It is something that originated with MMOs
Tanking, in the sense of misdirection and causing your enemy to focus on one thing at the expense of awareness of another, is an integral part of both tactics and strategy as taught by almost every military in the real world. Any time in history that a flanking attack has worked, ever, is because someone else (probably infantry of some sort) successfully "tanked" the enemy.
That nitpick aside, I get what you mean, but you really don't think blocking is valuable in D:OS? It doesn't seem that status effects can trigger on blocked attacks, which - at least until late game when you're just immune to everything - seems pretty handy to me.
