Is Instagram doing the same as Blizzard but with complementary apps?

I've played World of Warcraft (WoW) for several years some time ago, I started to play the game since what gamers call "vanilla version", so I experienced a lot of the game's growing, several expansions and features were implemented on my time there.

One thing that I've always noticed is the amount of add-ons that WoW has to improve many mechanisms and interactions inside the game (because it was like Blizzard never played his own game), so the community of developers and gamers took those problems and published add-ons to fix what Blizzard didn't.

Of course, was a matter of time that Blizzard make their move and include those add-ons functionalities into the game, and killing those add-ons. So basically, what Blizzard do is wait for some add-on to have some kind of success (many downloads and stuff), analyze what it do, and then include it into the game like a new feature, smart!.

Today I read about Instagram launching a new app called Layout, where you can combine several pictures into one and then publish the result to Instagram if you want, and before this, there were (still are) many apps that do exactly that. So that makes me think, is Instagram doing the same as Blizzard?

I thought many times to write some add-ons for WoW, and what happens if my add-on have success, it will be included in the game in the next patch/expansion and all my hard work will be forgotten? or maybe, Blizzard will try to hire me, who knows? And by saying this, what will happen will all these Instagram's complementary apps (or add-ons), all their hard work will be included in a future Instagram app or they will be acquired?