What is the difference between minecraft version 1.7.2 and 1.6.4?

I run a minecraft server an am currently trying to push a downgrade; However, players on my server fear the changes in features between the new versions without knowing what exactly will change.

I believe downgrading to 1.6.4 will be a great help for plugin/mod compatibility but I don't know the changes between each version.

So what exactly is the difference between 1.7.2 and 1.6.4

http://www.lmgtfy.com/?q=minecraft+version+differences

Seriously, how difficult was that?