Hi,
Just a few years ago, AC had a requirement of 35,000 miles for star gold (elite), and no requirement to fly AC metal. Over the past few years, AC has been tightening up their FF program to make the requirements more difficult to meet, also adding the condition you mention to fly on their own metal.
There were numerous threads a few years ago talking about possible MR's on United/Continental/US Airways that concerned obtaining AC status the quickest and cheapest way possible. I suppose you could just say that it's been changed in line with industry standards.
A3's program probably won't exist in the same form forever, either. And there are many other airlines that are changing their programs in favour of a dollars spent system, rather than miles flown.