Tire Pressure; Should We Inflate to Higher PSIs as Air Temps Drop?

While searching through the archives for information on tire pressure,
I came across reference to this table:

http://priuschat.com/forums/attachment.php?attachmentid=15137&stc=1&d=1243769222

I'm not sure I understand what the recommendations are meant to
achieve.

The table seems to say that for consistent inflation at different air
temps, you should be using higher pressure at lower air temps. If I'm
reading it correctly, it uses 70 degF as the standard air temp. As an
example, for 38 psi at 40 degF it recommends inflating to 41 psi.

I know that tire pressure drops ~1 psi for each 10 deg drop in air
temp. From that understanding, I expected to be adding air to my tires
as the air temp drops... back up to the target pressure, I thought.
What I did not anticipate is that as the air temp drops, the table says
that I should be adding air to get a higher target air pressure.

If tire pressure itself isn't constant with temperature, then the
recommended air pressures are meant to achieve a condition such
that the effect of the internal tire pressure is constant.

What is the constant effect that the changing recommended tire
pressures achieve?

Does it have something to do with higher pressure = greater number
of "air" molecules in the tire?

Yes, I did read the article accompanying the table here:

http://www.aa1car.com/library/tirepres.htm

 

donee, Wayne,

Thanks for your concise replays; it now seems obvious and simple.

For reasons not now clear to me, I just couldn't get the simple message
the table was meant to Illustrate... so much work, surely there was
some subtle, heretofore undiscovered truth... Not!

 

Oops, ddoouubbllee ppoosstt.