Well, many people do find burning flags offensive as well. That's a different question from whether it should be illegal!
Heinrich Heine famously wrote "Where they burn books, so too will they in the end burn human beings." a century later his writings ware torched at the Opernplatz in Berlin, among many other books.
Curiously, that famous (and prescient) quote was from a play referring to the burning of the Quran.
That it is within the legal rights of people to do so, is a testament to a great legal system we have, that people are actually doing this abhorrent act, is very disturbing.
I honestly don't know if Terry Jones, et. al., realize that they are following in the footsteps of history's most ignominious figures and movements by doing this. I have to believe they are just ignorant of history-- willingly or not.
Its hard to believe that they've found a way to burn a Qur'an in a way that is offensive not only to Muslims, but also to Jews and Christians-- the two groups who are most portrayed as "at war" with Islam.
In today's world, there is zero chance that any organization could ever hope to remove a "book" from the world. Further, this group first purchased all the copies of the Quran only to burn them (this actually helps make printing Qurans profitable).
There is so little similarity between today's world and the world in which book burning put ideas at risk... and this is so clearly a publicity stunt, that I can't even remotely bring myself to get irritated by it.