I really liked the random tables in earlier versions D&D, because they were useful for building a dungeon without too much effort (and without a computer). For eight years under 3e, I had to come up with dungeons for my players and honestly I am not that creative, so those random tables really helped to inspire me. My solution is to keep the old rule books handy and adapt the results to 4e. I also will look to other resources like Jeff’s little book.

From the in-game perspective, any trap in the place will have been put there by either the original builder or the later residents for some purpose. It will not be random. It will be put somewhere the trapmaker wants to keep others out of or away from. It won’t be somewhere the trapmaker and his/her/its friends need to frequently travel, unless it’s a magical trap that can be “keyed” to not function against them.

From the out-of-game perspective, if you’re designing a dungeon, isn’t setting down traps a part of that? Why on earth would you let it go until the party is actually inside and then leave it to the fall of the dice?

From the system perspective, 4e made a conscious choice to make traps less “wandering damage table” and more an actual part of an encounter, so random traps don’t really fit its philosophy. That said, there’s nothing preventing anyone from working up their own table to whatever standards work for them, if they so desire.