Interesting. I've never had those issues with our glass top and I use cast iron exclusively.
I also have never had any of the burners damaged by spillage and I openly admit that I do not clean after every use.
And am a huge cooker, and a rather frequent spiller.
In fact, when we bought this house (a foreclosure) the burners were in bad shape and I thought the stains were permanent, but I removed all of them with a cleaner called "Bar Keepers Friend."
Maybe there are different qualities of glass top, which might explain the big variance in experience.
I have no clue, I've never purchased one, just purchased a house with an existing glass top.