This is my tank for Combat Commander
With the 1st Ed. those tabs held the damage the monster had (i.e. wounds).
FFG decided that there was no need to spend money on a new mould for the monster bases and just used the same one they had from the 1st Ed.
There's no reason why you really need the tab, you can still place the ID Token on the base to identify monster A from monster B.
Besides the obvious cost savings, my guess was there was some thought put into trying to match the v1 components since they were planning on advertising that you could use your v1 stuff in the game.