Spam? Scam?

Once again, annually without fail, Reader's Digest has sent me a letter notifying me that I have been the selected few that are eligible for their S$125,000 sweepstakes. Then they will always send me a reply form to ask me to subscribe to their magazines. It seems that I will never win anything if my reply is 'no'. Come to think of it, I never heard of any winners being announced so far. Is this form of publicity and advertising legal? Don't the relevant authorities look into such things?