You can play 4E just as easily with the 'Core 3' as you could with any previous edition. There is no more expectation to use all the books as there was any time previous. Since you apparently have never learned how to play 4E, you might not have realized this fact. However, it is still true.
You are correct that I don't play 4e. The reasons for that are not relevant (I'm trying to sidestep any Edition War issues). I was trying to present the viewpoint of a non-4e playing D&D player looking at 4e at this point. Between different, apparently incompatible versions of 4e such as the PHB and Essentials being sold alongside each other and the large amount of splatbooks, and the apparent need (or so I hear it often said on these very boards) for a DDI subscription, the "barriers to entry" seem a lot taller than they were when I first got into D&D in 1998 and everybody I knew was playing AD&D 2e and all I needed to buy was the "Core 3" books.
I keep reading how it's so difficult or near-impossible to create characters without DDI because there is so much "crunch" to keep track of. Before DDI and 4e, that wasn't an option because very, very few games used every single book.
In my 1e experience, characters were straight out of the PHB . . .and maybe Unearthed Arcana. 1e lasted ~11 years from the release of the PHB to the release of 2e.
In my 2e experience, characters were made with the PHB and maybe a relevant campaign setting book or splatbook. 2e lasted around 11 years from the release of 2e to the release of 3e.
In my 3.x experience, characters were made with the PHB, and maybe a couple of splatbooks or campaign books. I only saw talk of using "every" book in CharOp/MinMax contexts. 3.x lasted as a "current" edition from August 2000 until June 2008, that's a shade less than 8 years.
I have no 4e experience, but I keep seeing talk about how characters are made with every book and how you need DDI to keep it all straight, and this isn't in a CharOp context, it's in regular gaming talk. 4e has been current from June 2008 and ~3.5 years later I'm seeing talk about waiting for 5e to reset everything again.