*sigh*
If someone feels that the DDI is sufficient for him, he won't _be_ an Essentials buyer. Everything from Essentials will be in the DDI, too. So that point is moot.
Obviously only someone interested in buying printed books will buy 'Essentials' books _or_ 'Non-Essential' books.
DDI is not entirely an either/or proposition compared to printed product. I mean, yes, it CAN be. But it can also be used as a supplement to the printed products you DO buy. A DDI customer
might not be interested in Essentials (although I suspect the "weapons grade nostalgia" aspect will attract somewhere between some and lots), but someone who buys into the game with Essentials may very well get a DDI subscription down the line. And that means access to the online tools.
Down the road, if/when WotC sells out of the PHB, they'll have a choice to make. What it comes down to is whether they think there's sufficient demand to reprint the PHB 1, and even moreso, whether there's sufficient demand to justify the expense of putting a corrected and updated version into production.
Bear in mind that most of the rules content will already be in the printed
Rules Compendium. Several of the character class builds and races (or versions of them so similar as to be basically indistinguishable) will also already be in print. Reprinting the thing as-is does nothing but confuse the only people who might want it - those who start with Essentials and want more builds.
Producing a brand new version of the PHB that includes all the updated content is more expensive, and a good portion of it will already be in print. That's a product for the people who already have the PHB 1, but would anyone buy "Fourth Edition Revised?" It's a little unclear who
wants that product. Clearly those who start the game with Essentials aren't going to be interested in a reprint of PHB 1 except (maybe) the class builds and (maybe) some magic items. Going forward, the combat rules may never again come in the same product where you get class builds. The exception to that is probably the stripped down versions included in the Red Box.
So if what's the PHB offers is pretty much about the class builds and their powers, it may make more sense to just do a
Heroes of... book that basically reprints those old classes, rather than reprinting the whole PHB. The point I was making is that whatever WotC does
print-wise, all the PHB class content (complete with errata no less) is
already available on D&D Insider and will continue to be so. Which means that the PHB classes will continue to still be supported
without any print product whatsoever.
Now, it could be a long while before WotC runs out of the PHB's they've already go, so this whole line of discussion may be (almost) entirely moot.