Believe it or not (I love sentences that start that way!)
Believe it or not, windscreen/window glass in the UK is quite different to that in the US. Solar-reflective glass is still something of a rarity there (ironic in a country where airconditioning is so common). But it is fitted to damn near (if not every) new car in the UK.
Perhaps car polish would damage the coatings?
Of course, you will always have the issue of getting polish on the windscreen surround and ending up with nasty dull grey bits.