No where on the page do they link to the start of the original story. The 'source' button links to the page/paragraph that the quote is from, but that isn't exactly the same as linking to the front of the other article.
The only links in the content go back to other Engadget stories. I'd say its bad etiquette.
This is a truly disgusting practice. The good thing about it is that once you know what’s going on, it’s relatively unproblematic. Whenever someone directs me to Engadget I know where I have to click. (In a funny twist, once you know where it is, finding the source is actually easier than when it is hiding in the article text.)
They do tell you the source, but leave it as an exercise to the reader to find where it is.
So this isn't bad etiquette so far as the group they're conforming to is that of other journalists.