How does it suggest that? It just says he doesn't want to turn his reviews into a book; I can think of lots of more plausible reasons than "because the most recent is the last one".
(The existence of this about-my-review page isn't reason to suspect he's quitting, either; I think he's been doing such pages for a while. I certainly remember there being one for his last OS X review.)
Note that the link loads a full conversation but scrolls to the end. If you scroll up, you'll see a pretty definitive statement that he's not continuing the reviews.
It's not very obvious unless you've seen a lot of similar links from Twitter, so I can't blame you for missing it. I just thought I'd point it out so you'd know what's up for the next time.
(The existence of this about-my-review page isn't reason to suspect he's quitting, either; I think he's been doing such pages for a while. I certainly remember there being one for his last OS X review.)