Hold the "S"

I have a theory. People from Iowa (Iowan(s)) do not say most s's that come at the end of a word.

Examples:
Des Moines - pronounced De-Moin or dɪˈmɔɪn (from here) notice no S in either word.
This is the capital and largest city in Iowa.

Defense - pronounced defen(d?), notice the S is not only dropped, but a
possible d has been added.
This is from the Koyote game. There were random Iowa fans in the
stadium and when they cheered "Defense!" They actually just said
"Defend!"

Blackhawks - occasionally pronounced blackhawk.
Same idea as defense.

If you have any example to support or a valid defense (haha) to add,
feel free.