It would be a terrible idea for the government to treat certain journalistic entities differently than others by way of reduced cost services. If too great a financial dependence on government exists, the media might be less inclined to run stories casting the government in a negative light and would sacrifice their independence.
No, the government should not cut postal rates for some newspapers, because then the government is in the business of selecting winners and losers. If the government picks who wins and who loses, effectively there is state-sponsored media. There is enough media through blogs and the web that the public still gets plenty of information about current events and social issues.