By the same token, the method of storytelling is also completely different because you don't have narration (or if you do, it's considerably less than it is in prose -- unless you're Don McGregor in the 1970s, anyhow...
), and you do have visuals.
The use of narration, whether by an omniscient narrator or by a character in internal monologue, seems to be less common in comics that it used to be. Heck, back in the '30s and early '40s, pretty much every panel was described with a narrative caption even when it didn't need to be. And Stan Lee's comics were loaded with his distinctive, lively, fourth-wall-breaking narration, a style that Marvel (and to some extent DC) followed for decades.
And is it my imagination, or are thought balloons becoming less common too?
You're not wrong, Christopher... thought balloons are almost completely gone as a storytelling device in modern-day comics. It has a lot to do with the current school of thought of making the art tell as much of the story as the words on the page. If it can't be told through dialogue, the current generation of comics writers will instead have the artist show what he intends to convey rather than spell it out for the reader.
About the only time I've recently seen thought balloons used was in Brian Bendis' run on The Mighty Avengers
, something of which much ballyhoo was made since he wasn't known for using them much or at all, even before it became the aesthetic choice du jour