See the part that is bolded? That part is false. We have companies who specialize in nothing but gaming machines, with all the bells and whistles. Hell, even standard name-brand manufacturers bundle games with new machines.
As for tech demos, have you seen the software nVidia cards come in? Half their shit is basically that.
You have to convince me here. Haven't seen a gaming PC with anything other than windows installed. Which is great for people who prefer to customize or format and start from scratch. What if you are new to PC gaming? What bells and whistles do you get?