Nintendo UK managing director David Yarnton said the feature, which extends multimedia and games from Xbox 360 to smartphones and tablets, hasn't been built "from the ground-up" like the Wii U's second screen.
"Our whole package we're looking at is integral, as I say, combining the game," he told Digital Spy.
"Really, our first and foremost part is for people to have fun playing games. We've added the other aspects - say, the entertainment factor - so that it makes it much more flexible for the developers, but also flexible for our customers when using the product."
Yarnton added: "It's been designed from the ground up the whole way through, rather than adding things on."
Xbox SmartGlass debuted at Microsoft's E3 press conference, and was demoed with HBO series Game of Thrones and concepts for Madden and Halo.
Microsoft later confirmed that it would feature in all first-party games.
Yarnton also said that further features will be announced for the Wii U, and that it has learned lessons from the 3DS launch.
The Wii U received a full specs and launch game list at E3 2012, and showed off a revamped Gamepad with analogue sticks and near field technology.
> Read our hands-on with Nintendo's Wii U launch line-up
> Read our full Wii U interview with Nintendo UK
Watch a video of the Wii U Gamepad at E3 below: