Why does ATI underclock their components?

[Lunch of Kong]

Question from a friend:

why does ATi underclock their components on purpose?

for example...the 9500 Pro had 3.0ns Ram on it...that means its rated for 333MHz. Why underclock it at 270MHz?

This brand new 9800 Pro has 2.0ns Ram on it, that is 350MHz, but they underclock it to 340MHz. samsung's spec on the ram they use say 350 is the rated speed....

I can kinda see the 9500 Pro being dumbed down so it doesn't cause to much competition for the higher end cards...but the 9800 doesn't make any sense to me.

[Lunch of Kong]

In ICQ, he just added:

I can certainly understand the chip itself being locked down to a certain spec...but why not lock the memory to the rated spec as well....

if you are building the top of the line card, why not do everything you can to make sure its way out infront of the competition, even if its only 10 more MHz, over 70 more 3DMarks?

[XPav]

To lower power requirements, heat, or so that it properly interfaces to other components on the board.