For some it's worth paying the extra to get the extra content and security of having it permanently. Pretty much all the Marvel films have had iTunes Extras added to them now, which provide things like documentaries, behind the scenes, digital comics etc. But, yes, saw that Netflix has an abundence of superhero movies at the moment and Sky TV (and therefore Now TV by extension) now has a Superhero Movie Channel for a short time with all the Marvel and most DC movies on.
Also available on Amazon Video https://www.amazon.co.uk/Captain-America-Civil-Chris-Evans/dp/B01L7Q7OMC/ref=sr_1_3?s=instant-video&ie=UTF8&qid=1524641794&sr=1-3&keywords=captain+america
Wish they would upgrade to 4K but we will probably have to wait for Disney’s service
Not permanent but if you want to see it now, it’s on Netflix also