Why would the 25th level Fighter drop his sword into lava? Last I checked, the only way for a character in 4e to drop his weapon is willingly.
How about Dominate? Isn't free actions like dropping a sword "at will"?
How about "Drop your sword into the lava Fighter, or I drop the Princess into the lava. Bwa ha ha ha."?
How about Fighter drops sword in his square in order to have a free hand, enemy slides Fighter, walks over and grabs sword and drops it into the lava.
Or, Fighter with sword and shield is on a rope bridge. Bridge collapses. Fighter has choice of dropping sword into lava to grab bridge with free hand or he drops himself.
This is also something 4E doesn't do well. Certain types of rules plausibility. Is it plausible for a Fighter to drop his sword into lava? Yup. In fact, it can make for a very challenging adventure. But, there are several "this isn't fun for the players, so 4E won't (typically) allow it" missing rules such as NPCs unable to grab items and steal them, PCs not dropping held items on the ground when they are stunned or unconscious, etc.
4e magic items (and even things like familiars) are as much a part of the PC and nearly as hard to get away from the PC as the PC's arm.
The amount of player entitlement (i.e. I am entitled to not have an item be destroyed or lost) is higher in 4E than earlier versions. This entitlement might get equated to fun entitlement by some people, but I don't view it that way. It's actually the rule system trying to enforce certain play styles on people.