This issue affects XP as well, when using tortoise SVN for example, I have to his refresh nearly every time to see the changes made to the files
Though maybe for some reason on certain 7 machines it's worse than on others.
The folder refresh is a rather lazy low priority affair which is probably on purpose to balance the OS's use of CPU and disk. Extreme up to date information could result in Explorer being unfairly piggish on resources.