No, there's no cross purpose, you're attempting to make a false comparison. An email client is specifically designed to access a remote server, you can in theory point it to a corporate intranet as well and that would work just as efficiently. A twitter client is specifically designed to access the twitter API and therefore is bound up to the twitter service which is an internet based application. These are intrinsically internet (or corporate intranet) in nature.
Whereas Elite Dangerous is fundamentally non functional without authentication and validation from the Frontier network servers, you don't get to choose that, you're not offered a choice either in how you access, whereas if you have issues with tweetdeck or thunderbird, you can always pick another client that works with the relevant API's.
To be clear, you will not be able to modify the client without breaking the EULA and risking an account ban, you will not be able to cheat in singleplayer mode, you will be affected by other players regardless of your chosen mode, the Elite Dangerous client as of now is no different than the client used for say MMO's, and therefore acts as always on DRM.
I suspect this will go in circles

right now ED has DRM, the login launcher bit. I'm guessing this was to ensure only alpha/beta backers could actually play. After all why back beta when you could just download it and play.
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If the login was moved from a launcher to the menu, allowing the use of offline functions (tutorials) then I would consider ED to be DRM free. In the same way tweetdeck would be. The fact that there is no access to the galaxy (online) without an internet connection and a login does not make ED DRM.
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Imagine there was a tweetdeck game "twitter rap battles" where you competed in 140 character rap battles with other players over twitter (hey, that's not a bad idea!... I'm off to kickstarter!). Assuming you had a login to twitter, if you didn't have a net connection, you couldn't play the game, not particularly because tweetdeck couldn't authenticate you, but because the game
is being on line, how can you have a rap battle with yourself (without being labelled a nutter)?
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DRM is a sensitive issue. There have been terrible implementations in the past, things like only being able to install the app once, or on one computer, or more than 3 times ever. Those were terrible no doubt about it.
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I wouldn't consider, having to be online to play an online game DRM. If they provided an offline mode, but you still had to be online to authenticate the game throughout,
that would be DRM (and bloody stupid), but the online solo isn't DRM.