I'm sorry, I was thinking of the 15 inch models. They have quad core processors and GPUs. The 13 inch models have dual core processors and also do not have dedicated GPUs. The app that I am used for the first screenshot, Mactracker, available in the Mac App Store for free if you already have a Mac, does not explain how either of the levels of 13 in MBPs could have 1536MB of shared video ram. It just shows up to 1 GB of shared RAM. I'm not saying the App is infallible, but I have no reason to doubt wither the app or the screenshot you provided.
What does seem curious to me is the the computer with less overall system RAM gave up more video RAM for sharing. 1536 MB of shared RAM for the Intel HD Graphics 4000 onboard video lines up with mine, so that makes some sense. Really, I would expect the shared amount of video RAM to be based off of the processor, but since both are the higher end 2.9 GHz dual core i7 instead of the lower end 2.5 GHz dual core i5, they should be equals.
My 15 inch MBP starts up the dedicated graphics card when I open programs like Google Earth, Aperture, or video games, and also with an external display. It works great for me... When it is using the integrated graphics, it also works well, but then again, in those situations it doesn't need gobs of power in the graphics department. I frankly don't know how well it would work in more intense situations without a dedicated card. The 13 and the 15 inch computers all can drive the same size displays, so yeah....
Here's the screenshot of information for the mid 2012 13 inch MBP...