Oh goodness no. The 100 games was just because technically they could do it, not that you should or will actually play games with 100 civs. I very much doubt they will balance for that or that will be taken in consideration for hardware system recommendation. Though I bet you'd need a beefy machine for it to run well.

I hope this gives an idea of what is meant by a recommendation of XXBG. As a general rule, when I bring up my PC and before I start any non-automated task (I have Win8.1, Start8, and a sidebar app in which I run three temperature and usage monitors) Windows will consistently allocate just over 2GB of RAM by the time it settles down. The amount allocated seems to vary a little (+/- about 10% to 20%) from boot to boot, but it is always more than 2GB on my PC. Out of a specified requirement of 4GB that leaves between 1.6GB to almost 2GB for a game. So the answer to your basic question is that when a game developer says "minimum RAM required = 6GB", they are saying that their game will run in their most minimum configuration of game options just fine if you have 6GB RAM on your PC. If you wish to use more than their simplest configuration (larger maps, more players, more population centers (like planets in GC), or more units) then you might need more memory. The only way to tell is to monitor your paging rate while playing the game.

During Beta (and the Alpha before it) GC3 includes all of the optional tracing and debugging code that the compilers they use provide that the devs believe is needed to debug problems that get reported to them. Some of those optional debugging and tracing options will be turned off for the production of the final release (but not all of them) which will reduce the size of the final product and the extra memory used.

Beta 2 (V0.42) on my PC has used from 1.8 GB to 2.4 GB just to get to the start menu, even when skipping the intro (which doesn't seem to take much memory anyway). A tiny galaxy game has taken an additional 0.4 to 0.5 GB, and a large galaxy game has taken an additional 1.5 to 2.0 GB, just to get a new game started. Adding these all together and you can see where you need between a minimum of about 4.5GB to over 6GB for a game. Yet to be seen is what the larger galaxy sizes will need, and how much all of this will be reduced by trimming down the debugging code and memory requirements for the final release.

It is a sure bet that 100 players will require more than the specified "minimum" or "recommended" amount of RAM. At this point, how much is a huge question mark.

But why show us it can be done if its just for show? I personally would like to be able to take on more than 8 or 9 opponents! perhaps its just me?

In the 3 October dev stream the devs talked about large numbers of civs in play at one time on the final base game. There were references when they were talking about galaxy size, when they were talking about the UP interface (ie, how the reason for most civ information on the UP interface being shown via hover text being because the alternatives wouldn't be feasible for 100-civ games), etc. So it's not just for modding.