I think the problem with a Marvel or DC Jump that collected the core titles necessary to following the goings-on in the respective mainstream superhero universes is that the readers would only go for it if it were significantly cheaper than collecting the individual issues, and there's no real incentive for Marvel or DC to do that. And if it weren't any cheaper, readers would balk at being "forced" to buy the comics they don't want in order to get the comics they do. It would be a lose/lose.
I think Ed Liu has a good point about American comics being a slightly different proposition from manga in that the emphasis is on the single issue as the collector's item, whereas in Japan the single issue (as collected in an anthology like Shonen Jump) is considered disposable; if you want to collect the series, you wait for the tank (the rough equivalent to what we in the U.S. call trade paperbacks).
And I think that the appeal of collecting the tanks is enhanced by the fact that in most cases, you have the prospect of eventually having the complete series to display on your bookshelf, because no matter how long-running a manga might be, it WILL eventually end when the creator's interest and/or lifespan run out. Whereas mainstream American superhero comics are not tied to their creators, but designed as perpetually ongoing series that seldom really definitively "end" but are only ever "canceled."
So you've got a situation where in both the U.S. and Japan the creative, storytelling side of comics has grown up around the business model and vice versa, to the point where they've become difficult to extricate from one another. In Japan, you buy the anthology if you just want to read some comics on your train ride to work or school, and if you find something in there that you really like and want to collect, then you buy the tanks. In the U.S., you buy single issues both to read and maintain for your collection, and the TPBs are there to help you catch up on anything you might have missed.
The other issue is that a DC Jump or a Marvel Jump would be an anthology of, ultimately, very similar titles. Part of the fun of an anthology is that it's a grab bag: you might buy it for one or two flagship titles, but once you've got it in your hanRAB, it lets you check out lots of different stuff that you might not have done otherwise.
There are definitely American titles that I think would be a better fit for an SJ-style anthology than the mainstream superhero stuff; self-contained, creator-driven stuff like Sandman, Bone, Fables, Hard Time, Y: The Last Man, Ex Machina, etc. I'm sure there are many more (including more current ones than, say, Sandman) that I just don't know about because I'm not as in touch with the American comic scene as I used to be. I'd love to see stuff like that collected in a weekly or monthly anthology that I could pick up now and again to check out what's new and what I might want to consider collecting when the TPB comes out.