I'd like to point out an inaccuracy in your post:

Quote - Most of who play games are teens or kids, you cannot expect them to have money to purchase a very expensive top level computer.  So in the end, most of who play games use old or very old computers and if the game maker doesn't support old computers his sales will be very little limited to only some adults that play games or some priviledged kids.

This is from a 2005 ESA demographic study:

Heads of households that play video games: 75%

Average game player age: 30.
35.0% under 18 years
43.0% 18–49 years
19.0% 50+ years

Keep in mind this data is 2 years old.  The average gamer age has been increasing internationally since the study was conducted.  For example, in Australia 2005, the average gamer age was 24.  In just two years, it has risen to 28.   This type of increase is reflected in the U.S., U.K., Japan etc....

Since the average gamer is in their late twenties/early thirties, they have more buying power than kids and teens.   Because they come from a generation who has grown up with video games and is far more comfortable with utilizing sophisticated technology and adopting newer ones than any previous generation, they are capable of making informed decisions about hardware purchases.    They can afford to, and do purchase at least mid-range level hardware if not leading level hardware.

Your conclusion that "most of who play games use old or very old computers" because they're too young to afford anything better is inaccurate given the demographics.