Well, I think the hard role approach to D&D is a little misguided. My parties have rarely had 4 people in them nowadays, and you end up constraining concepts, and even game worlds to make place for roles, which I think puts things backwards.
Mostly I (and my friends) find traps appallingly boring. Barring particularly adventuresome traps described in places like Dungeonscape (or Indiana Jones) they are just speedbumps that get in the way of "real" adventuring. I also don't like the gameplay they encourage, namely a kind of cautious forensic form of D&D. This is a taste thing, so ymmv.
More generally, as a DM I do try to tailor things if characters' abilities are off the beaten path ability-wise so to speak. For instance, if someone is playing a very social character in my D&D game, I'll probably include some more social tidbits. This is a long time ago, but a friend was running a game and we had a Factotum for the first time in one. So, he threw in tons of skill stuff b/c, I imagine, skills are often something that gets kind of lost in the stabbing and magicking that tends to define D&D.
Note that this doesn't get anywhere close to "neutering" the challenges. First off, that's a category mistake. The combat characters are good at fighting. Ok, but the fighting can be more or less challenging. They can be facing Glooms and Elder Titans or Goblins armed with pancakes. The same logic applies to anything else.
All that being said, I don't usually do all that much tailoring. I like to present the illusion that the world is what it is. I'd be annoyed if all the sudden my fire mage is coming across a suspiciously high number of fire resistant monsters. So, I try to just keep with challenges that fit the milieu and tone. So, no, I wouldn't suddenly jack up the number of traps (which to be fair, is usually and transparently set to nearly 0 in my game worlds out of personal taste) just b/c nobody played a Rogue.
The above tailoring tries to calibrate to what is interesting to the people and characters in the game. Someone playing a social character is telling me "I want to do some social stuff." Social stuff usually fits in any milieu -- sentient beings aren't that hard to come by -- hence the accommodation.
All that's on the DM side of things, which is a little orthogonal to the original point that Wotmaniac was making and PlzBMC was reiterating. On the PC end of things, roles are quite easy to cover. Just taking trapfinding as the motivating example, PCs without a dedicated trapfinder can circumvent them any number of ways, though, so it rarely matters much. (Although when you're committed to circumventing something, that's not a good sign that it's a fun-filled action-packed part of the game, hence my above comments.)
So, it seems silly to me that somebody fills compelled to play a Rogue-type just to account for them. I think trapfinding is an easy case. Healing is often thought of as a role, too, and that one is also not that difficult to account for, too. I've found that condition removal is a little tougher to manage, given the variety of maladies that float around in 3E D&D.
That does require, though, that people commit resources to doing so. For instance, setting aside my personal antipathy for traps, if you decide to build a party without a cleric or a tank or whatever you simply need to account for that. Maybe you have a summoner, who has a ready substitute for the tank. If you don't do that, or the players aren't sensitive to that, then things get dicier. If people aren't approaching the game with that kind of troupe design, I could see the need for the harder approach to roles. Although I wish D&D was less hidebound about them in general.
