Well for one, the article never specified anything about private text chats (unless I missed it?) so I think you're asking a misleading question. Most of the article was about the US government/FBI looking to read public data, which AFAIK has never been protected by wiretapping laws.
Additionally, something that is different is the scale. In the US, an activity may be legal if done once but if done millions of times it may be illegal. Here, there are many times more people plotting, discussing, and celebrating terrorist events online than there are on traditional phone calls. Having phone calls be traditionally 1-1 and private internet chats be 1-many, even 1-1000000 or 1 to 7000000000 if public, is a totally different beast. I'm not sure there is any analogous previous laws, I think we need new laws.