Large machine construction and temperature control

The following reference in a previous post got me thinking

>>> http://www.scaled.com/services/cms_mill.html

A friend of mine works with the aerospace industry doing QC fixtures for 3D
tubing. He is constantly telling me about the tolerance these giant milling
machines work to. The thing I don't understand is, for a machine that large
one would thing that just expansion due to temperature fluctuation would
cause the machine to go back and forth several thousands over a whole tool
path over time.

Can anyone address how the manufacturers of these kind of machines manage
this issue (other than spec'ing that the machine must run in a controlled
environment?

Do those of you who have built larger (NOT as large as the above) CNC
routers, plasma tables find any problems as a result of heat expansion of
machine parts?

Just curious,

Ken Jenkins