My best guess is that the ARB guys are doing this. However, knowing the cash is limited to $70M they would likely recieve a combination of cash and shares. They could offset the risk by shorting ABH knowing they will get shares back shortly to replace and make a nice, hedged return.
That could explain the ABH downside recently and supports my line of thinking to manually transact.
I actually thought that was a good idea (and bought the shares before reading the fine print closer...), but it doesn't work. The amount of cash that's available is prorated based on the number of shares tendered, and the share part of the offer isn't worth as much as it used to because ABT is down since the offer was made. So no way to make easy money (unfortunately...)