The teaser lately seems to be teasing events further away than the next movie.
Cap 2's teaser teased Quicksilver/Scarlet Witch/Strucker ala Avengers 2 AOU rather than a Guardians teaser.
Well one reason is because we already got our Guardians teaser in
Thor: The Dark World. Of course, that would support your point even more though since Captain America 2 came after Thor 2.
Looking at past post-credit teasers:
Iron Man - pretty much teases Avengers with Nick Fury informing Stark about the Avengers Initiative
The Incredible Hulk - again, kinda teasing Avengers with Stark informing Ross about a "team is being started" (despite Marvel now kinda pretending that the 2008 Incredible Hulk movie doesn't exist because of the whole recast thing)
Iron Man 2 - Coulson & crew find Thor's hammer, which directly sets up the next movie (IIRC this post credit scene was even in the Thor movie itself)
Thor - Erik Selvig and Nick Fury take a look at the Tesseract while Loki is shown to be controlling Selvig. Obviously this sets up Avengers, but one could also argue that it helps set up the next film (Captain America) with the Tesseract's first appearance.
Captain America: The First Avenger - I don't even need to explain this one, the post credits scene is an actual scene from the Avengers and it segues straight into a freaking trailer for the Avengers
The Avengers - Doesn't really set up a particular film, though I guess one could argue GotG. I would say it really just sets up the future of the MCU. (oh and the shawarma scene sets up nothing lol)
Iron Man 3 - Tony Stark is babbling while Bruce Banner is sleeping. ok
Thor: The Dark World - Sif and Volstagg deliver the Aether to the Collector. Once they leave, the Collector then proclaims "one down, five to go". Obviously sets up GotG, seeing as the Collector is even in the trailer for it. (oh and the second scene after the credits just shows Thor coming back to Earth so that he can make out with Jane)
Captain America: The Winter Soldier - hydra has loki's scepter and avengers 2 characters ok (second scene just shows Bucky learning about his past life at the museum)
Guardians of the Galaxy - AGE OF ULTRON TRAILER!?!?!?