Just because the airline says they won't refund your ticket doesn't mean they don't have to. Know your rights. If you don't rebuttle their refusal then basically you "accept" not getting a refund because they told you they wouldn't.
If your flight is delayed due to weather...IE
Snow storm keeping all flights ground
Fog is keeping all flights ground
Severe weather keeping all flights ground
Airlines generally do not HAVE to refund your ticket. They will reroute you then or for a later date or give you future credit on a flight. But don't expect a monetary refund. They can't control the weather. Since you paid for their services they are required to deliver...hence...future credit or reroute.
If there is a mechanical problem, the wing fell off...or the engine won't run, that is negligence on the airlines part. Its not your fault their plane isn't running. They can be made to refund your ticket. They will tell you they can't for reasons a, b, c, and d. But airlines aren't exempt from law and regulations.
Generally most airlines will offer reroute, or future credit (based on your current fare value, not a free ticket) on a flight. If you accept this...wonderful for them b/c basically you agreed to this compensation in lieu of a refund. If you continute to ask for a refund, if under the right circumstance..you can get it back.
FYI...Delta has the WORST customer service of any airline. They have taken to much pride in this merge with Northwest. They have had several customer issue complaints and are only recently cracking down on it.