There are research universities and there are teaching universities.
Research universities have graduate programs and their focus is on doing research. This means most professors teach one or two classes (some have 0!) but have other obligations.
Teaching universities on the other hand don't typically have graduate programs (if they do, it is just a Master's program) and the professors have full teaching loads (I think 3-4 courses is the norm) with little expectations to publish.
For example, Austin Peay State University, where I did my undergrad is considered a teaching university. Every professor has a full course load and not a single one of the professors I had has published in the past 5 years.
UPDATE: chronicle.com defines teaching university as one where professors have "a standard teaching load of four courses a semester", from Interviewing at a Teaching University.