For one Gruber is lampooning WSJ's entrance into the Apple rumors business, so keep in mind he might be mentioning those "specs" in jest.

And for two, it should be noted that competing devices released in the past year have higher density displays. Also higher density displays allow for better looking user interface. I would imagine Apple wouldn't want to be outdone in either respect.

In short, I don't think we should draw conclusions neither from Gruber's post, nor from the densities of other devices Apple may be selling.