Exactly. I totally agree that one is always free to skip filler episodes to get to the main plot, but that only applies to completed series or series that have a lot of episodes already. When you're watching a series that's currently running, seeing a new episode has been subbed only to see that it's just filler can be seriously annoying, especially if recent episodes have left off on a cliffhanger. It just means a whole nother week or more of waiting.
Fillers can be done right though; for example, when I was watching Katekyo Hitman Reborn I didn't even realize that there were two arcs of filler in there, and even when I did realize I still watched it because it was enjoyable and was still somewhat relevant to what was going on. It's when the fillers are like Naruto and completely random and irrelevant that make them aggravating. I'm still asking myself to this day why I even bothered watching 100 episodes of filler when I could have just skipped to Shippudden : P