That's true. The posts where the wipers are mounted are always prone to early icing and since the Pilot's can't see the wings, without going back into the cabin and looking out a window, the wiper post is a very useful visual indicator of ice accumulation.
Even if Anti-ice was on, and I have to believe that it was, it won't provide unlimited protection. That's why you never fly into "known" icing conditions for any length of time. American lost an ATR (high wing Turbo Prop.) in Indiana, that was put into a holding pattern in icing conditions. After that accident American shifted all the ATR's down South to limit their potential exposure to serious icing conditions. Despite that crash, no rules were ever adopted to keep aircraft out of icing conditions. FedEx just lost an ATR last week in Lubbock Texas, that could have been caused by ice.
The FAA and more recently the NTSB are becomming so politicized that even when the final cause is known, the chances of preventive rules being enacted are going to be very slim.