One of the comments on the post ragging on buff spells was that magic swords are technically buffs, since they add a bonus to the attack roll. But I'd argue that no, they aren't buffs, or weren't at first. Just because something improves your odds when performing some action doesn't mean it's a buff. After all, we all recognize that polymorphing into an ogre is not buffing. A magic sword is, like that girdle of giant strength, an item from traditional tales and literary fantasy. The +1 bonus it provides is a mechanic that supports the vague suggestions in the source material, that a magic sword makes you better able to defeat the dragon; the idea of "defeating the dragon" came before the idea of "improve attack rolls".
However, the +1, +2 and +3 swords in D&D did lead people to start thinking in terms of "What other bonuses could we add to magic swords?" and "Is there a +4 or +5 sword?" In other words, although I don't consider a magic sword to be the same as a buff spell, I do consider later elaborations on the magic sword to be the same kind of annoying thing as the ever-expanding list of buff spells. It's an invitation to focus on the game system, instead of on the events and elements of the fictional world.
I'm toying with the idea of changing the way magic swords work, but I haven't quite settled on a good replacement yet.