Luckily, I doubt this will be a regular trend- probably the reason they could justify selling a piece of DLC that requires another piece of DLC was because Cats and Dogs has been their best selling pack so far.
Also it is extremely versatile when it comes to adding extra stuff (like small pets); something like Get Together would never get this treatment, because there's nothing extra that is could feasibly be added.
It's annoying though how features we got in one pack for The Sims 3 now has to be broken up into a piece of DLC that requires another piece to get access to every piece of content - but saying that, I don't want to jump to any conclusions until I see the trailer and LGR's review.