Originally posted by mee Adding seals and charging 50 more makes sense to me
It might make sense to you, but apparently not to Pentax. Nor to any other company, otherwise Nikon, Canon, etc would all add WR to all their lenses, if it was all that easy!
You assume it's an easy matter. But I encourage you to think about the engineering work required, then the testing (drops, vibrations, shocks, general performance, thermal and humidity testing, etc), eventual iterations, repeats, then put in place the new manufacturing line, with production tests to certify the lens complies with the company's requirements.
It,s a bit more complicated (and expensive) than just "adding seals".