Nice to see that stirred up some lively debate.

The thing is, many folks who started with basic D&D stayed with Basic D&D, hence it becoming very successful as its own line as BECMI (and even before that, B/X). The gradual process of tiered, expanding boxed sets demonstrably works; more recently, Green Ronin has done very well indeed with its Dragon Age sets and these follow the exact same model. Can we really same the same for all the “taster” sets that have been released for D&D since?
Note, I didn’t say “No.” in the absolute sense to a boxed set (quite the opposite) but I did say the idea of a stripped down “taster” set wasn’t not a good idea unless you went the BECMI route (bitesize portions, gradually expanding the game, the rules rewritten specifically for the younger audience).
The problem is, unless introduced by an existing players, RPGs are dependent on being *read* and the number of folks prepared to read and learn such a game is limited. Making a game smaller helps, but at the same time how many youngsters would read such a slimmed-down set and then suddenly be okay with reading the meaty tome that DCC is a few months later? I’d say “Not many.” Bear in mind the serious competition rpgs have now that they never used to in the entertainment and games markets.
I’d also ask folks (especially the other parents here) to really look at the DCC RPG and ask themselves this question: is it (and its modules, including all art) really a game you’d give to, say, a 10 year old (the age I learned, on my own, with Mentzer Basic D&D)? I love the game, but I’d argue it’s an adult game with adult themes that isn’t necessarily appropriate for younger folks (and I'm a Brit, so adulthood is at 16, btw). And if you argue that a DCC Basic set would be for folks “13+” or something like that, you’ve just shot yourself in the foot with a hellishly narrow age range, because by the time they’re 15-16, if they’re the sort of kid who’d happily read and play a tabletop rpg, they’d be able to read the core rules anyway. Also, don't forget, producing such a work has to be cost-effective and not just the result of rose-tinted wishful thinking. Better to write a game specifically for youngsters if you’re trying to introduce them to gaming, though that is also a road paved with, if not outright failure, then a lot of success that didn’t grow the market the way some daydreamers assume it will. Heck, I was even involved with one such rpg (Faery’s Tale Deluxe) that was nominated for three ENnies and an Origins award! Didn’t make much of a splash.
The idea that a boxed set not produced by WotC or Paizo can somehow “grow the market” to any appreciable degree is, sadly, a pipe dream, especially as fewer folks read, those who do read less (or only online), bookshops are folding, more shopping is online, and folks interested in fantasy/sci-fi games can get a quicker, more attractive fix with a console. Hell people, they don’t even read the short instruction manuals any more, which is why games often include as-you-play tutorials. Going the electronic route idea has more potential, but only if it was fully-interactive in a way no traditional rpg pdf has been to date; a LOT of younger folks already live their lives attached by umbilicals to their hi-tech mobiles or pads, and numbers are increasing.
If folks want to grow the traditional market, they need to get out from behind the computer screen and start local clubs, recruit more non-gamers, and teach their own sons and daughters (and their friends). Anything else is simply wasted hot air.
Once upon a time I'd have been one of the folks calling for a starter boxed set. These days, after freelancing, after studying publishing and marketing (BA with Hons), after self-publishing, and now being well into my second decade of teaching, I think it'd be a great way to throw money away unless you're in an enviable position already, and maybe even then.
Colin