I'm curious to know how some of the code in my organization is working and was deployed as the code coverage is less than 75% for many of the triggers/controllers.  

I see that the creation date for most of the code is 2011.  Is this a recent requirement Salesforce implemented? (i've only been working with SFDC for about 4 months).  I know if I deploy code with less then 75% coverage, the code will not deploy. 

It would make sense to me that SFDC implemented this requirement and allowed code in production to continue to run even though the coverage was less than 75% but going forward would force developers to meet the requirement.  Any insight that can be provided would be of great benefit to me. Thanks!!!