After shooting any handgun, I spray it with a preserving gun oil like RemOil and wipe it down with a soft cloth. This helps remove fingerprints, and leaves a coating that can help eliminate finish problems. I also store guns in bore store type products. They are a silicone impregnated woven sock that helps repel moisture.
Straw is one of several methods of establishing an iron oxide coating on metal surfaces. Like rust bluing, salt bluing, nitre bluing and flame bluing the objective is to form an oxide other than rust (Fe2O3). Since the surface is oxidized once it won't be oxidized a second time in the same spots, preserving the surface.
Straw is not an applied coating. When, over time, other oxides form on a strawed surface they are much more visible because they are almost always dark in color.
Good article on iron oxidation is at:
http://en.wikipedia.org/wiki/Rust
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.