The "more RAM is needed" thing is pure unfounded bullshit.
If someone is only interested in mining scrypt or vertcoin (At its current N factor), I will say you are correct. Vertoin's N factor will eventually change (at the same pace as glaciers move - across land)
On other coins, that increment their N factor regularly, some are up to N=14. If you get more than 2 cards that run 4GB each, you'll want to have 8 GB system ram. The miner software has to allocate the scrypt buffer in system memory to start, and allocating a 3.5 GB buffer for 3, 4, or 6 cards just doesn't fit into 4 GB of RAM.
I just fired up 5x R9 290 cards at N=12,13, and 14, with 4GB of system memory for several minutes at each N. Seemed to compile/load the kernel and hash fine. This might not be the case on windows, mind you - I run a custom gentoo install on all my rigs.