this is an old article written about $20 for $20.. interesting read
http://www.thestar.com/business/2012/07/05/coin_collector_learns_the_difference_between_legal_tender_and_spending_money_the_hard_way.html
but keep in mind, this is an old article and the mint had work hard to fix this.
This is how I looked at this... if you go to a corner store with $100 bill, it is legal tender, does the store have to take that $100 bill??? They still have the right to say, no sorry, we don't take $100 bill. Actually, if you live in Canada, good luck getting the new bills (plastic bills) to work with vending machine.
So, these $20 for $20 or $100 for $100 coins are the same. It is legal tender, it doesn't mean the bank or stores will have to take it