Actually, that is half correct: For Space Marines and similar, the special rule is attached to the equipment. Thus, by having the equipment the special rule applies to the unit.
For the best example of this in action, see Vanguard Veterans, especially the Blood Angels version. They do not have Jump Packs by default (they're Infantry), but the moment they buy said Jumppacks they become Jump Infantry, complete with the special rules for 'Jump Infantry' (and for BA: the 'Descent of Angels' rule too).
Thus, for the Tau suits, the same applies: By having the jet pack, Tau units get their 6" jump move and 6" assault jump move
But note that not all special rules of this type are attached to equipment: Rough Riders and Hounds of Chaos are both Beasts, and Daemon Princes are Jump Infantry... but the rule for such are directly attached to the model itself and not any equipment they're holding (a Rough Rider horse is not classified under "equipment"
)
Similarly, there's a curious, slight difference between the Feel No Pain between Death Company (built into the model), Ork Nobz with Painboy (built into Painboi's equipment) and Dark Eldar (built into pain tokens, which is a DE army wide rule). If ever there is a wargear which switches off equipment (similar to how C:GK switches off daemonic gifts), the Nobz will be affected, but the Death Company and Dark Eldar will still merrily ignore wounds on a 4+.