I have been wondering something for several days and finally found my answer. No, I still don't know if or why the US thinks or doesn't know if pasta is a weapon! But at work we have a bucket to collect Coke can tabs for the Ronald McDonald House and I have been wondering why not the whole can? Surely that would get you more money faster. So I Googled and was getting worried because I saw a lot of folks on Yahoo Answers and myth-busting sites that said this is a myth, it's not worth it, etc. Then I found the source I probably should have started at:
(This is from the RMH website)
"Ronald McDonald Houses collect pop tabs instead of entire aluminum cans because the tabs are pure high-quality aluminum, unlike cans, which consist of aluminum and other alloys. Tabs are also easier to store than whole cans."
So I'll continue to save them, unlike sending email forwards upon discovering snopes.com!