Not sure the steel wool actually removed scratches as someone else pointed out. May have removed paint transfer from the wiper blade or arm.
But the glass does get quite a bit of build up over the years on it. Steel wool, possibly a light application of the Mr. Clean Magic Eraser (be careful with the Magic Eraser, may want to test it out on an old drinking glass or jar before you get hard into your glass on your car) and rubbing compound and a buffer will easily clean and polish the glass. I have even seen people use corn starch as the final buffing powder as well. I have even seen people use sand paper to remove pits in glass fog light and head light lens. Starting with coarser paper, then moving to finer and finer grits. Not sure I would advise this on a windshield where optical clarity and lack of distortion is important.
Cerium is also the same stuff that is usually used for rock polishing as I recall. You may be able to pick up Cerium powder at your local hobby store and make it into a tooth paste consistency for deeper scratches? Cerium paste and buffing wheel may be needed for deeper scratches. But be very careful about localized heat build up when buffing or polishing glass with a lot of pressure and something like Cerium as you could have a problem with stress cracking due to uneven heat expansion. Just do not keep the buffer/polisher on the glass in the same spot with a lot of pressure for an extended period of time. Come of the glass with the buffer/polisher and let the glass cool between polishing.