OK so I did some research.
Scientifically adding salt in the boiling water is to prevent discoloration. It does not raise any water temperature; water boiling point is always 212F/100C. Discoloration occurs due to the release of oxidase when cut or expose to the air or heat. That's why we soak fruits&veggies (like apples, potatoes, artichokes) in (sometimes acidulated or salted) water, right?
Especially green vegetables contain chlorophyll. When we boil them, magnesium within the molecules are unbound by heat then chlorophyll oxidizes. But this green guy, chlorophyll can be stabilized by sodium ions of salt.
The idea, according to the chef, was that if you don't salt the ice water bath for cooling, then the salt that the veg has absorbed from the blanch will want to leave the veg while it sits (osmosis). Its the same idea behind brining something, is that the area of high salt concentration will naturally want to move to the area of low salt concentration.
In this sense, salt concentration in the ice bath should be lower than the one in boiling water. But how long do we keep the veggies in the ice bath? Maybe 5 minute is not enough for withdrawing the salt. I will kill my cooks to leave veggies in the ice bath too long.
Thanks everyone to post your comments. I learned a lot I still not agree with adding salt in the ice bath. Jeffrey Steingarten should address it in his next book!
Oh, on another note, I found that boiling pasta in salted water is to give more chewy "bite" to pasta. Since pasta is made of strong gluten wheat flour, salt will tighten areolation (fish net like structure) of gluten and give more elastic texture.