well.. you think your going to play any "modern" games on 128 mb your sorely mistaken
i'm sorry to say, but i agree with 1.5 times rule.. why? well, depends on what you buy your computer for, if you buy a 128 mb ram computer now, you obviously not going to play much new releases.. to understand that, you have to know what is swap space used for.. and where the swap file is stored in.. The reason for RAM is to have a place to store and retrieve files FAST.. harddrive can be 10+ times slower in I/O than RAM.. when your playing DOOM 3 on a 128 mb pc, no matter how much swap you give it, you can't play it, you just can't.
if your system RAM is 32000 that means it should be able to be accessed at about 3200 MB/s where as that virtual memory cannot even acheive 200 MB/s, even on a super fast harddrive (but seriously, if your going to spend money on 10,000 RPM harddrive, might as well get some more RAM no?)
when you say 1.5 times is not a good min guideline, i still have to disagree with you.. An example of 4 gig ram and 6 gig page file is NOT a good case for you.. it all depends on what you use your RAM for.. when your getting 4 gig of ram, your obviously living in the future, so when shelling out that much money for 4 gig of ram, i assume whoever does that have a pretty demanding app.. such as intensive webservers, which demands whatever memory it can get it's hands on, so yah, they ARE probably going to use 6 gig of page files
This is the same as telling me 4 years ago that when i have 512 mb of ram, i don't need 1.5 times page files.. which i very much do right now
now why do you need virtual space? well, it's that if you occasional use a massive program (such as editing a huge TIFF image), or when you sometimes opens alot of program.. if you regularly tax your virtual memory, then your surely better off getting some more RAM
so to conclude, how much RAM you have determines what program you use, it doesn't matter if you have 2 gig of virtual memory, you won't be running DOOM 3 anytime soon on 128 RAM