There's a couple of reasons that a higher rez map is important for SR2020...
1) With all the playing being effectively on the 'world map', it was important to bring the world level resolution up from SR2010. In the 2010 maps, a number of smaller maps had good resolution for the imagery, but the world map reslution was relatively poor. This made it hard to see mountainous / hilly terrain, coastal features, etc.
2) One goal for SR2020 is 'looks better'... might not be important from a gameplay standpoint, but this factor is important for a lot of players (and potential players). I recall some discussions in other wargame-type forums where I asked people "what's more important, eye candy or gameplay"? They would almost always answer gameplay, but then a bunch of them would play the SR2010 demo and post "it doesn't look all that great".
We're pretty confident that we can make the higher rez maps run without too much of a performance impact - the minimum specs for SR2020 are higher than 2010, but that's as much because of the increased world map size as it is the imagery.
The unanswered question, as mentioned in the blog, is what impact it will have on the game size - we're going to try to keep this down, and possibly even experiment with JPEG or other photo-compression on the imagery, so that the digital download version won't be huge.