You don't always need a missed block, but if you do, there are alternative paths to aquire missed data.
So, how do you know that you missed a needed block?
Double/tripple/etc broadcasting does not solve the problem. When is the block repeated? 8 hours later? What if you are off the grid for 24 hours, or just happen to be off when the rebroadcast occurs. The issue is not "unlikely" the issue is: the system is not 100% guaranteed.