A Rogue is just a Thief in 3e/4e/5e clothing; and even if he never in fact steals anything he still has training in *how* to steal, training that most other classes do not get. Same could be said of a Magic-User who for whatever reason never casts a spell, or a Fighter who gets by on guile and charisma rather than violence; they both still are what they are.
Not sure how the 3e rogue is "trained to steal". He's trained in those skills he places skill ranks in. He may know how to Open Locks - did he learn that in the form of picking locks, or constructing locks (so all locksmiths are thieves)? Perhaps he knows Sleight of Hand - did he learn that as a pickpocket or a stage magician?
Forgery seems geared to theft, but do most Rogues/Thieves put ranks in it? Bluff would be the skill of choice for any con artist, but seems like it goes to a lot of other classes. Did you learn to Climb as a cat burglar or a mountaineer? Hiding and moving silently lend themselves to many activities besides thievery (every Special Forces operative is a thief?).
Seems like most "thief skills" are also used as "non-thief skills". Pathfinder, in combining some of those skills, further watered down the "thief" argument, most notably merging Open Locks with Disable Device.
Class is the tools the character has. The four archetypes have Arcane Magic; Divine Magic; Martial Prowess and Skills. I could easily see a 14 INT Human Rogue (11 skill points per level) never putting a rank in a "thieving skill", depending on the build. Let's see:
- he's agile and athletic so Balance, Climb, Escape Artist, Jump, Ride, Tumble
- he's perceptive, so Spot and Listen
- he's a social butterfly, so Diplomacy, Gather Information, Sense Motive
He's not even stealthy, nor does he have the ever-popular Use Magic Device. Show me how he is a Thief.
I recall our party Rogue (as I recall, this was back in 1e) watching our party Cleric remove a necklace from a skeleton, only to be attacked by an apparition of the dead owner. After it was vanquished, the Cleric was complaining of his wounds and the Rogue told him it "serves you right for being a disgusting grave-robbing Thief ".