Agreed. WotC have a tough choice: put some quality material in the DI, and be accused of "forcing people to sign up", or don't put quality material in the DI, and be accused of short-changing their customers.
However, I
still think I would prefer larger and more expensive core rulebooks. Make them really big and full of stuff, and you minimise the amount of stuff I have to lug around to my weekly game. (I know that sounds backwards - but most supplements only have about 5% used at any time, which means carrying a lot of 'dead' weight. Bigger core rulebooks means, in theory, fewer supplements, which means, in theory, less weight in total.)
But hey, I know that's not actually going to happen. Maybe one day, instead of a 4.5, we might get an "Expanded PHB"? That would be nice, I think.