But why does Apple need to produce its own giant TV screen to improve the user experience?
A screen is a screen, it just shows whatever the HDMI or WiFi signal is sending. The logic and software is mainly in the attached boxes (game consoles, TiVo, AppleTV...) and the cloud.
Picture quality is already very good today, so is TV design. For example, movie buffs not satisfied with LCD can still get top-of line Plasmas from Panasonic. Attaching a box is easy, plug in HDMI cable, done.
Where is the added value of the TV set (flat screen part) for Apple and consumers?
I see why Apple can and should improve its AppleTV box in the future, but why produce a screen?
PS: There is a reason why Apple stand-alone monitors never have been big sellers and probably never will be.