Rust is rarely a problem for me. I try to keep blades clean and dry and treated. If rust does develop, depending on the type of blade and value, I deal with it accordingly. I have cheaper users like Machete's that I don't really even worry about, some good use and a quick cleaning will keep most of the rust in check. With a higher quality blade I remove the rust and re-treat with a protectant. Contrary to the practices of some, I store my knives in their sheaths and rarely experience any issues due to that.

As far as why they coat the blades... it's cheaper than polishing and protects the steel a little better when not in use. Rust isn't much of a problem on a user blade, but it's hard to sell a carbon steel blade if it starts to rust before it's sold or used. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />