Why do you keep recommending stuff that have large amounts of bad reviews and low ratings and low power? Do you want my computer to run Windows 3.0 or something??
It's based on personal experience. He builds a fair number of machines and has found that this combination works for him and gives him satisfied customers at a reasonable cost. I have a different bias in that I prefer reliability so have a tendency to go for a different set of cost / benefit.
Reviews can be useful but you have to be very careful with them. The publisher depends on getting advertising dollars and ideally free systems to review on the companies submitting product. Also to sell magazines, page views etc. they want to give the idea that something is new. If you are an established company that has had good reviews in the past then there is less temptation to submit your product or for the product to be reviewed. No one really wants to say this design created the year before last is really solid and still is good value for money.
Memory is a case in point with aggressive timings. Yes you can get 2% more performance out of them by spending twice as much but in the big picture the bottlenecks are more to do with switching textures in and out of the graphics card. Having 640 Mb of memory on the graphics card no matter what speed cuts down that bottleneck.
Trainz works by running through a series of instructions. It is much more complicated to divide up the instructions over multiple paths unless the system is built that way so currently Trainz like most games or Sims is only capable of using one core or CPU at a time. Work is being done at Microsoft to make using multiple cores easier but at the moment and for the next five years it isn't going to be main stream. The graphics cards on the other hand handle things differently. What are called pipes are in fact CPUs and nVidia is releasing software that enables you to do scientific computation on the graphics cards in parallel much faster that it will run on the CPU.
For the moment on a dual core the operating system can sit on one doing very little say 5% utilisation, Trainz sits on the other at 100% utilisation. On a quad core the operating system sits on one doing very little at say 5% utilisation, Trainz sits on another at 100% utilisation, and the other two sit there doing nothing except giving off heat which is why the dual is clocked faster than the quad, getting the heat off the cpu is the limiting factor for performance.