During the weekend many people were ready to get games on sale when steam servers fell apart due to low maintenance. Because of all the snow where Steam is headquartered, the employees have not been able to come and keep the servers up.
Many people are going to miss out on good deals due to this. The only way to save people's hopes of getting good discounts is to extend the sale by a few days so that people can get on and get their games once servers are maintained again.
Valve shouldn't be able to use a snowstorm as an excuse to scam people. So the sale should be extended to make it all fair.