These new updates match numerous practices that Apple has implemented on the iTunes Movies store starting with the launch of the Apple TV 4K in September 2017. With the rollout of 4K support in iTunes, customers' back catalog of HD movies were automatically upgraded to 4K where applicable, and Apple promised all new 4K releases would remain at a competitive price of $19.99.
Apple never specified that SD movies were getting a boost to 4K, but some users have noted that select films upgraded from SD to HD to 4K over time. Still, other users have not seen any updates to their SD iTunes movies, perhaps due to missing rights from certain movie studios, so Google's promise of both SD and HD upgrades to 4K should be an easier transition for those with a bunch of old movies in the Google ecosystem.
Google will also notify users when their movies are upgraded to 4K, and point out which ones were upgraded in the Play Movies and TV app, which is a feature that iTunes lacks at this point. For Apple users curious about this aspect of their film collections, the third-party Cheap Charts iOS app [Direct Link] has an "Upgraded to 4K" section with a reverse chronological list of films that recently received the picture quality update in iTunes.
Apple struggled to get Hollywood's major studios to support 4K films at $19.99 -- and Disney still remains notably absent from any 4K support on iTunes Movies -- but eventually many of the major studios backed Apple's decision. The same appears true for Google Play, with new films from studios like Sony Pictures, Universal, and Warner Bros. available in 4K at $19.99 and under, but new Disney films like Incredibles 2 are only listed as HD compatible.
Additionally, Google announced that users can now watch content in 4K using the Play Movies and TV app on most 4K Samsung Smart TVs (in addition to previous support for 4K Sony Bravia TVs). The company says it's working on adding support for LG TVs as well. Lastly, the smart TV app for Samsung, LG, and Vizio TVs has been updated with a modern look and feel for an overall "better experience," according to Google.
Google has been expanding its Play Movies and TV app throughout the year, in March introducing a feature that accumulated content from numerous streaming services into one centralized watchlist. Similar to Apple's TV app, Play Movies and TV now lets users discover new shows and movies, and find which streaming service to watch them on, adding all of the content into their watchlist. In this area, Google notifies users when content is available to buy and rent, if the price has dropped, and if it's now available to stream.