Email is completely different since it allows people to communicate with one another while RSS just acts as an asynchronous communication tool. Every major online communication breakthrough (IRC, IM, etc) succeeded because it handled communication in a many-to-many relationship. RSS on the other hand is simply a one-way 1-to-many relationship and this is what will prevent it from ever making it big and changing the lives of people.
For me personally, RSS is not a communication tool anyway. It’s an information tool. Something that allows me to go through huge amounts of data without spending much time or effort.