The third is just noting that a jQuery function doesn't work in some contexts.
The fourth and fifth (which, like #1, are two lines from the same comment) are just documenting a try/catch block because something jQuery is doing might throw an exception.
The sixth is legitimately working around a browser issue, but it's not something you'd need to worry about unless you wanted to write that jQuery function. Like, it doesn't actually cause problems — it's just necessary to make that jQuery function return the exact value that they want.
The seventh is just an attribute named "support".
So far it looks like this isn't actually a list of reasons you will need jQuery, but a list of places where the string "support" occurs in the jQuery source. The fact that so few of them actually have anything to do with the compatibility of client code kind of undermines the point the author is trying to make.