[quote=@Raineh Daze]
<Snipped quote by IncredibleBee>

There's actually one thing that's the problem, though, from the example I've been thinking about: what if something IS magical, but the magical effect is simply making it physically more durable? I've not been proposing that magic makes something inherently undamageable. More a 'is it ignoring the magic'.

I think we've been arguing over two separate points.

[/quote]

Well in that case the increased physical endurance is a side effect of the magic. Since the Dragonslayer cuts through magical stuff, the item would be relying solely on its own physical durability, and if that weapon is a common weapon made of common materials, it wouldn't hold out for more than one hit.