Historically, Apple has had third-party gadgets in their actual stores and in the web store, considering there are a lof of gadgets that can be used with your iDevices.
However, some have noticed that fitness bands and trackers have been disappearing from shelves on the heels of the Apple Watch announcement. Some of these removed devices include Jawbone's UP24 band and Nike's Fuel Band. Nike has had a great relationship with Apple until the Apple Watch rumors started, reports Mashable.
The Apple Watch will largely feature a native health and fitness tracker system, explaining why they don't want any third party competition.
Apple didn't elaborate on the reasoning behind the move but told Mashable the company is "constantly evaluating and making changes to our merchandising mix." (viaMashable)
According to VentureBeat, the Apple Watch contains "both fitness-oriented biometrics sensors and software for tracking runs and other workouts."
Notorious fitness tracker FitBit was already pulled from shelves months ago when Apple found out FitBit wouldn't mesh with HealthKit, Apple's iDevice health system.