As some no doubt remember, Sonic & Knuckles provided back when it was released "lock on technology" which allowed it to connect to Sonic 2 and Sonic 3. Is this accounted for in the current generation consoles emulators, the Xbox 360 Arcade and Wii Virtual Console?
Yes, the lock on feature is present. Gametrailers mentions it specifcally in their review here.
Yes, the lock-on feature is completely present, allowing you to play Sonic 2 and Sonic 3 with knuckles, and includes the easteregg, which can be accessed trough a "fake" lock-on with the original Sonic the Hedgehog game leading you to the No Way? No Way! screen.