I think fillers just says something about what the anime studio thinks of the characters. They also try to make money, so you can't get around fanservice haha. XD
Fillers are probably more expensive than canon because it takes more effort. They have no manga as sketchbases and have to do everything themselves.
There are rules they have to follow with fillers though, basically stuff they put in cannot conflict with manga plot structure. The only real difference between the manga and anime is when Naruto met Utakata (the 6 tails Jinchurki) he never met him prior to being swallowed by son goku in the fight with Obito's six paths of pain. Now when the part comes soon for this battle, obviously there will be a fallback to the time Naruto met Utakta, just for clearity and consistency of how the anime progressed.
There are however rare instances where stuff that originated in filler came into the manga, some of this includes one of the 7 mist swords, Kiba,the lightning one first used by Riga in the pre shippuden filler arcs, made its first manga appearance in the fight against the edo 7 swordsmen. Gaara's "girlfriend" the one we see every now and then who always fawns over Gaara, she began in the filler arcs too.
But the reason people say filler does not count is because they are not always going to be based on the original material. The main purpose of fillers is to both extend the story with side stories aside from the main journey the heroes go on, also its the time when the anime team can be free to do stuff that the manga team never did, such as for instance, rather than make Sakura just go to Tsunade for training, they gave her a filler arc to give her more incentive for it. Another was the battle between Naruto and Sakura vs. Kakashi at the start of shippuden, what was once a simple short panel sequence, it became a full fleged battle for them to work with, where in the manga you only get a breif showcase of the new powers, I felt this short canon-centric filler was good because it let the audience know how the time skip treated Naruto and Sakura and what it lead to. In other words, some fillers are just extended scenes based on canon material, the Naruto and Sakura vs. Kakashi fight, tenten vs temari, Shino vs Kankuro, stuff like these were originally offscreen but gained the chance to be shown in the anime.
Some stuff like Sakura and Sai over-watching Naruto's wind style is an extension off the canon material, basically they added Sakura and Sai in just to watch from afar. This segment had a scene though in which we personally all liked, Sakura revealing how though Naruto has his faults, he proves them wrong and thats just who he is, this is a scene we like despite being filler and shows she accepts him for who he is despite his faults, this is one of the things we like about that episode.
Other stuff though can seem a bit too extended, I mean like ep 166, taking a short sequence of Hinata vs Pain and extend it to an entire episode with flashbacks, added drama and stuff for Hinata's character, but for times I still ask if doing all this for one episode was necessary. To me for back then, if Kishi really was serious about NH then the episode would have been much bigger on Hinata but I feel that because NH still has not shown anything overly serious, especially with manga developments like 631 and 635, makes me say that this was just an episode perriot went wild with, now I wonder how they will treat the episode holding chapter 615 later this year? Will they keep it simple or overtax a simple moment like this again like ep 166?
I will say this though: when the fillers add humor, I love to see the stuido run wild with the characters, they can get it out of their systems, put something into action here or there. Kinda like the NaruSasu kissing from one of the fillers when they both got stuck together, that was just building on the old early gag, likewise the filler where Hinata lost her eyesight, they trolled all the big pairings in that episode which made it a good laugh. Long as the fanservice is kept to a degree of control, Im fine. But the most important thing for fillers is to let the manga stay ahead, next week the canon episodes resume and we will see exactly how things turn out in the anime version.