I'd take your statement as a grain of salt as you are misinformed.
Basically take it this way, some companies offer better warranty/tech support, and generally those products are more on the expensive side. Especially in Nvidia's case its this. However some manufacturers differentiate from the reference design, and that makes them DIFFERENT.
Generally, manufacturers like Gigabyte, PALIT, etcetera prefer to redesign popular selling designs, in better forms, usually coming with better cooling and a better power phase.
Example, Gigabyte 8800GT Turbo Force vs normal 8800GT. Normal fries, turbo force doesnt, normal one has two phase, turbo force has a cooling running three phase, normal has a long PCB, turbo force has a shorter PCB.
These are just some of the benefits of non reference design GPUs.. IMHO reference designs generally are flawed by the chip maker's logic that if it aint broke dont fix it.