Just a personal anecdote (again), but we bought the redbox when starting out. It wasn't all that good, and while I did buy a bunch more books, I bought most of them used -- in part to guard against risks of disappointment, and in part because there is a huge price disparity on D&D books more than a year old.
Similarly, I have a DDI account, but just barely -- I don't regard it as a particularly good deal, in part because it doesn't provide online access to the books. If they want more subscribers, they need to either reduce the price or make it more appealing.
Yeah, I think it is hard to generalize on how people get started. I think these days a lot of kids may start playing with parents, but its still new young people getting into it and doing things with the game on their own and having fun that will ultimately grow more gamers.
I thought the Red Box was pretty ham-handed. I mean, it is somewhat in the tradition of previous intro boxes that TSR did, but those were BETTER. I bought Holmes Basic in 1976, which was the very first 'starter'. It had a book that had FULL rules, and play up through level 3 (though it was sadly a few years before TSR published the Expert book that had the higher levels). It had maps and a book full of treasures, plus the dice and a few other goodies. Some copies had the module "B1: In Search of the Unknown". Overall you could play with that set for weeks or months and not wish for anything more.
The 4e Red Box seemed a lot more limited. You could perhaps play for a couple weeks with it, but the adventure was much less substantial, the rules didn't match up with the regular 4e rules exactly, and there were only a couple classes, etc. It was kind of a weekend one-shot wrapped in a box really. Not a terrible deal at $20, but I think they'd have been better off to up it a few $ and had a better rule book, maybe some tiles, and a few stand up character cutouts, a few pogs for monsters, and a better adventure. As usual Paizo's starter box seems to have garnered more praise, though it is hard to tell if it succeeded in bringing in more gamers or not.
As to DDI, I guess if you are playing with only the HotF* books and an RC/DMK/MV you may not find the Compendium so much use. OTOH with all the 4e books in use I couldn't possibly live without that thing. I suspect there's no chance WotC will ever put the actual books on DDI, at least as long as physical books are an option. I could see a game that was ALL digital materials where you just subbed up and played, but I'm thinking it isn't likely cost much less than DDI does now. It just isn't cheap to generate all that material.