I have bought Vic2 and both expansions in the Apple AppStore. The 3 are independent downloads in independent folders and different app packages, and I think I did run A Heart of Darkness without installing Victoria 2 vanilla and A House Divided, so you could try to buy just HoD expansion (the one you need to play PDM mod, or PoD, as it's called when it runs on HoD).
In order to access the Vic2 forums in here (and get the 3 icons in your account) you will need to write to Virtual Programming support to ask for the keys, since they do not appear in the appstore bill nor in the game. You send them the billing info and they provide the keys to register the game and expansions here.
I run HoD v3.03 (QRPE) with PoD since the day that I figured out which PDM was good for me and managed to install it. PDM and APD (PDM for aHD) are no longer supported for their creators. You can get the latest PoD for v3.03
here.
Don't know how it runs in Retina displays, but it runs perfectly in my MBAir mid 2013 (i7, 8GB, 13" 1440x900).
Hope it all helps.