One Planchet Size/Weight, Three Different Denominations

I'm curious...

Canada's current crown-sized commemorative silver dollars have a weight of 25.175 grams and a diameter of 36.07 mm.

I recently purchased one of the 2009 80th Anniversary of Canada in Japan $5 dollar commemorative coins and found that it had the same weight and diameter as my silver dollars. After a bit of investigation in Charlton, I found several other $5 commemoratives that appear to have been struck on the same size/weight silver planchet -- 2005 Alberta Centennial, 2005 Saskatchewan Centennial, 2006 Breast Cancer and 2006 Snowbirds.

In 2005 and 2006, the RCM also appears to have struck three different $10 commemorative coins using "dollar" planchets -- 2005 Year of the Veteran, 2005 Pope John Paul II and 2006 Fortress of Louisbourg.

Has anyone ever seen the RCM publish/post an explanation as to why coins of three different denominations were struck on the same size/weight silver planchet? As they are all NCLT coins and their face value has little relation to their silver content, I don't view using the same planchets for three different denominations as too big of a deal, but it does make me wonder!

Anyone have any info? Do I have my facts straight?

Thanks in advance.