Are bees growing more defensive?

Recently, I've noticed a few US reports (here's the latest) about bee stinging incidents where Africanized bees have originally been suspected, but subsequently cleared after laboratory analysis. It may just be media interest in killer bees; it may be some form of hybridization of Africanized bees and the traditional European variety in some areas; or it might just be that honeybees are more aggressive than they used to be.

I'm not in an area where Africanized bees are ever likely to appear, but I do hear anecdotal reports from long-serving beekeepers that bees just aren't what they used to be. Could varroa cause irritability? Or too much hybridization? Or just a bad dose of Golden Ageism?