Most situations causing a delay are beyond the airline's control (this is called force majeure) and you are not entitled to accommodations or compensation. Some situations where you are entitled to accommodations are shown in the airline's Rule 240 (varies from one airline to another).

It is common to get accommodations if a flight is diverted or makes an unscheduled stop for reasons other than weather. Delays caused by holding the plane for another passenger or due to another unruly passenger, are usually compensable.

Sometimes airlines give accommodations, usually only to first class travelers, when they don't have to.

You should be able to find the airline's rules on its website although navigating to them is probably not easy.

Even if you are not entitled to accommodations, you can usually get a discount "distressed traveler rate" for a hotel stay just by asking an airline gate agent or customer service rep.

Travel tips:
http://members.aol.com/ajaynejr/travel.htm