Here's my take regarding your questions:
1. My guess is that the rock must have caused a chip or a crack in the wiped area of the glass. In many jurisdictions, this is considered a safety issue if the chip is large enough and will prevent the vehicle from passing safety inspections/regulations. If the rock caused any sort of crack to start, most jursidictions will require the glass to be replaced as well since cracks tend to travel and grow even though windshield glass is laminated safety glass.
2. Generally manufacturers use hidden or semi-hidden wipers to reduce drag and noise at highway speeds as well as improve the forward visibility. As you note, hidden wipers and the cowl area are more difficult to keep free of snow/ice in the winter in colder climates. I can't answer why the automotive engineers over the years have decidednot to provide a feature which ducts the internal defroster air to the cowl area but I assume it's because of the cost/complexity of keeping it clear and working vs. the perceived small benefit. There have been a few cars and trucks over the years which had defroster elements (or sometimes entire electrically heated windshields as Ford once tried) in the front glass similar to those seen on some vehicle's rear glass. The cost and reliability issues associated with these featuers seem to have made most of them go away. There are some aftermarket heated wiper kits as well as windshield/wiper covers you could try if you live in an area where this is a constant issue. I have no experience with them, so buyer beware.
The final solution to the ice/snow issue: Florida!
That's my take.