Along with upgrading the 15 inch Macbook Pro, Apple deleted the 17 inch Macbook from its Pro line of notebooks. However, at the same time, Cupertino giant also released Retina version of its Macbook Pro that is quite different from the non retina version.
Personally, I see the hardware in both models being the same, other than two major differences – screen resolution and type of storage. Both come with same graphics and same RAM clock speed 1600MHz. Even both can be equipped with quad core i7 processor that hum at 2.6GHz clock speed.
On the non retina, the resolution of 1440 x 900 can be upgraded to 1680 x 1080 which are still a lot of pixels to work with. On the retina model, the pixel resolution is 2880 x 1600. So, you can read a lot of text at a time by reducing the text size.
Another thing to keep in mind that with the retina version, the upgrade options are rather limited. If you are planning to upgrade the SSD to a bigger one, you will not able to do that on the retina one. On the non retina model, you can easily do that. Also, battery replacement is much easier on the non retina MBP as they are not glued to the casing, like in the case of retina MBP. In short, the non retina is upgradable internally after purchase, while the retina macbook pro cannot be upgraded after purchase.