The Apple screen, on top of being higher resolution, is also a IPS panel, which gives much better viewing angles as well as color reproduction. It is the only type of LCD suitable for photo/video work.
For a bunch of people who complain a lot about getting good value for your dollar (and how Apple doesn't do that), you sure are misinformed about the gear you're buying. I suppose as long as it throws some kind of image up on screen it's good right?
Nice that you assume I don't know what kind of panels Dell uses (currently e-IPS and S-PVA, 8 bit) while Apple hitherto was, to put it politely, not known for using quality panels in their offering (TN <cough> 6 bit <coughcough>). I'm glad to Cupertino is at least up to snuff when it comes to Dell. Took sure their sweet time doing that.
The only kind of displays suitable for professional work are the expensive kind that comes with an external calibrator. Neither Dell nor Apple sells these.
Next time, please don't assume people are ignorant.
So, no, the computer at the back is not exactly free.