"'FSX is a 32-bit application and it won't use more than 4GB under any circumstance""

Tho True, what some fail to realize is that aside from running FSX, Flight Simmers often run other programs along side FSX, which require more RAM (Memory) to make everything work seamlessly !

They may include :
Flight Yokes
Rudder peddles
Throttle Quadrants
Eye or head tracking tracking software
Screen Recording software
AI Traffic software
Weather Software
GPS Navigation software
Multi-Screen set ups
and a host of who knows what software & Hardware

For the Basic Generic Flight Sim user, the above statement may hold true ,,,,,

But for the rest of us who are Deep into Flight Simming with some pretty complex Aircraft, the more RAM and the high quality Graphics card and Higher Quality Processor is whats needed ~ !!!  8-)

I have a decent Quad core processor
2GB XFX Graphics card
16GB of RAM

I use 2 separate computers - 1 solely just for Flight Simming only
The other which is almost identical with a tad bit less RAM for everyday general purpose computing and Editing my Flight Sim Videos for YOU TUBE.

Jetranger
Sim Hanger on YOU TUBE