The new system won't have a record of your loot history or check your inventory. In your example, Bob might win the same item off of the boss every week (assuming he's running as the same spec each time).

The only thing the system looks at is 1) if you are eligible for loot (have you killed this guy already this week?), and 2) what your current spec is.
So you can win the same item over and over? Doesn't this seem like a waste of loot?

Loot gets wasted today if someone needs it who already has it (probably because they need everything), or if the game just keeps dropping the same stuff over and over. Some amount of loot wastage is okay -- we don't actually want loot accrual to be too efficient or players finish the content too quickly. On the other hand, we don't want it to be so frustrating that players give up. Slot machines need to pay off once in awhile, but not every time. :)

The new LFR roll system - Please explain