Team Fortress 2 has the following lines in Crafting Items menu:

• Smelt primary weapons (2 of the same primary weapon)
• Smelt secondary weapons (2 of the same primary weapon)
• Smelt melee weapons (2 of the same melee weapon)
• Smelt class weapons (2 weapons used by the same class)

All these produce 1 Scrap Metal.

So, why are the first three items needed, if 2 of the same weapons are always used by the same class anyway?