This is the one spot I think Essentials fails or at least is lying.
Well, that depends on your frame of mind.
We keep hearing that it's not there to replace the core rules but augment them.
...Insofar as people currently playing using the PHB DO NOT need to buy the Essentials Books to keep playing. You can continue to use your PHB-based dwarven fighter with no hitches right next to an essentials dwarven fighter and one won't be inherently more powerful than the other, or that Keep on the Shadowfell won't require extensive re-writing to make it work as an Essentials adventure (unlike say, trying to run Keep on the Borderlands).
The idea is that DDE is the new core, compatible with the old core, that doesn't invalidate the old, it just sets the baseline going forward. Not quite the same as a .5 edition (which invalidated the old core with new books) but definitely is the future jumping on point from here on in.
and we keep hearing that the core rules will be reprinted when the time is right.
They will. If they ever sell out of the core-books AND there is still demand for them. With Essentials out and DDi keeping updated lists, I don't see a pressing need for them except by people who want all the Essentials Updates in their Old PHB.
But if it's a straight reprint, even with errata, wouldn't that be ripping off people who already bought the rule compendium and the various heroes of x?
I assume WotC saw a need to make some changes to 4e and realized they had 3 options: New edition (nerdrage), .5 Edition (nerdrage), or separate-but-equal new core that can be swapped in at the DMs leisure, but we're going to use it going forward. (least nerdrage).
Now the problem is outside of the core classes/powers, there just isnt' enough content in the PHB to make it worth the purchase if you've bought the Essentials books.
Exactly.
If you own the major Essentials releases: (RC + HoFL + HoFK + DMV + MV) your not missing much from the PHB/DMG/MM trilogy. You swap druid for warlord, probably have a few different monsters in the MV, and don't get all the paragon paths/epic destinies (which is probably a good thing, thinking about daggermaster, pitfighter, and demigod). Otherwise, the core three is covered. If you really want the older material, its available but cavaet emptor: its OLD and outdated. Essentials is new hawtness.