I pushed the button

[Mike Abberton]

You do not have to upgrade the map to play anyone, as long as you both agree to play with the stock map and scenarios. Andrew Brown's map is a mod for WitP that extends the map a bit and redraws it to better reflect the distances between some common destinations.

There are also user-created scenarios written around the map that take into consideration a couple new bases that are present on the map. There are also several widely-played mods that make extensive changes to the mechanics of the game and/or the OOB of the various sides including:

NikMod - As I understand it, the NikMod changes the game's air model mechanics quite a bit to help make A2A combat less bloody and at the same time making flak much more effective at low altitudes to help force players into more realistic 4-engine bomber tactics (i.e. bombing from high altitudes). Combined with this are some tweaks to aircraft production and a host of other small changes. There are versions of the Nikmod for the stock map and for the AB map.

CHS (Combined Historical Scenario) - this is a huge effort that uses the AB map and a drastically revamped OOB to more accurately represent the various forces engaged in the war. There are also tweaks to the game mechanics in the A2A model and other things in CHS as well.

There are other mods out there, some historical and some "what if" types. From looking at the Matrix forum, it does seem like the majority play using some sort of mod, but there are still people playing stock scenario/map games as well.