But remember the OP's point that one of his players was insisting (well questioning) that the "wealth" value was only 1/2 because they were going to sell it.
The point I was trying to get to was that it was "their choice" and it wasn't like the items were "useless" to them. They were just "not preferred" which is entirely different.
I am not really seeing the choice here. Typically, you would sell gear only if your party can use it effectively. Else, the party would likely keep it. How would you define useless then? Because by your analogy, even a wizard could in theory find use for a greatsword, even if he is not proficient with its use, or wear armour, even when it obviously interferes with his spellcasting.
For example, lets say that the PCs are expected to get roughly 4000gp of treasure per encounter. Say the DM has to decide between gloves of str+2 or a pearl of power2. The wizard would have use for the pearl of power, thus they would likely hold on to it instead of selling it.
But say the DM gave them gloves of str+2 instead. The fighter and cleric in the party both already have one each. And the other 2 PCs (lets say 2 wizards in this case) certainly don't need one. But if they sell the glove, they get only 2000gp on spend on upgrading their existing gear (assume there is nothing to sell here), which means they are getting less gear that what they are supposed to have had the DM chosen to give them a 4000gp magic item they could use effectively in the first place.
Granted, it is not always as straightforward (for example, if you give the fighter a +2 weapon, you might need to factor in the money he may get from selling his existing +1 weapon, or the cost of upgrading it instead, assuming he does not hand it down to the next PC). But the fact remains that the wealth a PC gets can swing wildly depending on whether he decides to sell the gear or hang on to it.
The thing here is not whether he ought to have sold it or not. But now that he has sold it, what should be done with regards to the discrepancy in the suggested wealth guidelines that was created?