I would actually say the sugar itself probably doesn't need to be sanitized by boiling. Like with salt I'm guessing theres few beasties would survive in it. Having your sugar dissolved in water sure makes it easier to mix into your beer without having to stir the crap out it though. Hot water makes the sugar dissolve more easily, plus boiling it will drive out any oxygen that could oxidize your beer. Just my amateur guess.
Personally I have a 2 cup pyrex measuring cup. I fill it with about a cup of water, weigh out my priming sugar charge, microwave til its at a decent boil and just leave it in with the door closed until I get all my equipment setup and the like, then add tobottling bucket and rack on it.