Do you know why they won't? Because there is HUGE money in it! How many buy and sell websites based on PR? I think if the PR was eliminated, it would impact the web economy.
I see your point, but why would Google care about our, (little), economy. Most sites bought and sold on PR are almost never sites worth more than $1000.00. If I buy a small site I will probably buy it on the face of the PR alone, ('cause I'm lazy). Anything bigger and I will research the site properly, (like I should for all sites). At the end of the day, Google is not making a penny on those sales, so why should they care? FFMG