I'll just play Devil's Advocate.

Back in the good old days, Revenue Canada used to have big warehoues of millions of tax returns. It had to store these returns for seven years.

Let's see:

1) Cost of running a building

2) Cost of librarians to file returns so they can be found again.

3) Cost of destroying returns more than seven years old.

Methinks the taxpayer might have a bone to pick with the Luddites.