no, a lot of plot-driven comics have an actual ending. Sometimes it's because the author got bored or didn't have time to continue working on it, but usually it's something that the whole comic was steering at from the beginning. Like Queen of Wands, for example.
Most webcomics actually aren't one-shot gag strips like penny arcade or vgcats, the latter of which is the posterchild for ADHD-afflicted nerd humor. Most webcomics are also nothing short of fucking terrible, but when I get hooked on a plot comic I tend to obsess and sit there until I read all of its 200-600 strips.
I'd never actually caught such a comic while it was running until recently, but now I read
Girly with FREQUENCY. It's a plot comic that is largely cute and not too serious and is the sequel to cutewendy, which is the comic that spawned off of wendy which is the comic i started this thread about ok
I don't want to hear about how lame/gay/actually gay the comic is, I just thought I'd link it since someone would ask because their copy of google had overheated or something