The 15" is slightly less DPI. I was only comparing DPI because, to be honest, every laptop I've ever used that wasn't a Thinkpad or a Macbook has left me wondering whether I should just use pen and paper instead.
The DELL has a 15.6" screen, the MBP has a 15.4" screen. The screens both have the same resolution and aspect ratio. That means the MBP’s screen has a slightly higher DPI (221 versus 218).
They don't have the same aspect ratio. The Dell is 16:9 while the rMBP is 16:10.
They don't have the same resolution either. The rMBP is 2880x1800 while the Dell is 3200x1800.
