I am also curious about why not to use cast iron on the glass top stove? My husband does most of the cooking and he does use the cast iron on our glass stove top.
On another note, I did completely ruin my mother's old chicken fryer cast iron skillet before we had this glass top. I had fried the chicken and was making the gravy. Had the flour all browned and poured in the milk... cold from the refrigerator. A loud bang scared the crap out of me and then the milk was running out all over the stove. The bottom of that cast iron pan had split wide open in the middle, a big gaping crack! I'd made gravy a hundred times in that old pan and never suspected that could ever happen.