I don't use this, but looking at that list, I would disagree. I just looked up some of the top sites I'd want to use and I wouldn't have guessed any of them

Wikipedia -> !w

Youtube -> !you

reddit user -> !reu

subreddit -> !reddits

also !reddit points to new version, I'd want !redditold

Twitter -> !tweet

Steam -> !steme (???)

Twitch -> !ttv

That being said, if you're on DDG, there's pretty good auto complete on bangs so you can find it by typing the name and looking at the favicons.