For the first, D&D is a combat game. All the classes are designed with combat abilities in mind. It is expected that every character contribute effectively to the *combat*. They can also contribute in other ways. First edition didn't have any non combat abilities... except thievery. 2nd and 3rd had more, but they usually came at the expense of combat capability (the argument here about 'useless except for traps). 4e is doing even more to separate the two to avoid the gimp your combat for your RP stereotype. You can blame WotC design if you wish, but its the design this game is based on.
For the second, you are shifting topics. MY comments were directed specifically at your assertion that items shouldn't factor into DCs. That has nothing to do with whether or not wizards can run through traps. The saves bonuses from items are not that big a deal and both 3rd and 4th addition factor in assumptions about those items into their rules. Where items matter for traps is on the disarms and so on. If you don't factor +skills items into those DCs and use the pnp numbers, anyone buying the relevant skills *and* using the items is going to disarm everything automatically by early mid levels. The pnp DCs don't factor in +4 tools combined with +5 items because they don't exist.
What is it you want? The rogue to be able to do traps on elite without gear, feats, or enhancements, just class ability? I'm not trying to be snide with that. I've honestly lost sight of your position.