I'm pretty sure that a lot of weapons ARE the same now in terms of damage. The maul is 2d6, for example, and I'd be surprised if the greataxe and greatsword weren't 2d6 as well. The fact that the maul is a giant hammer and the greatsword is a giant sword will probably be represented by special abilities attached to weapon types and available by means of feats or powers.
Still, part of making weapons "feel" different is giving them abilities that actually occur mechanically. Some mechanical benefits will be better than others. For balance reasons, that means that sometimes certain weapons will need to do more damage than others. If Weapon X is a high critical weapon that does 1d8 damage, and Weapon Y is a regular weapon that does 1d8 damage, Weapon X is superior. It might be a good idea to reduce it to 1d6 to accommodate, or to provide a benefit of some other kind to Weapon Y.
Still, part of making weapons "feel" different is giving them abilities that actually occur mechanically. Some mechanical benefits will be better than others. For balance reasons, that means that sometimes certain weapons will need to do more damage than others. If Weapon X is a high critical weapon that does 1d8 damage, and Weapon Y is a regular weapon that does 1d8 damage, Weapon X is superior. It might be a good idea to reduce it to 1d6 to accommodate, or to provide a benefit of some other kind to Weapon Y.