Vista 64 sp1 & sp2, slow file copying, why?

I do like Vista mostly, however there are some things that really seem to annoy me and I want to take the opportunity to ask if there is a natural explanation to my issue below:

With both Sp1 and Sp2, copying (cut command) a 700MB file from my already spinning, secondary internal harddrive takes only a few seconds to move to my new external harddrives (my 3 external USB2 harddrives), but I counted just now, it takes 20 seconds for the file transfer dialogue to go away AFTER the bar indicator shows that the file has been moved over.

Why is that? Is there a natural explanation for this slow file transfer? System resources were all available for the file transfer, with no auto defrag or anything from what I can tell

There is no reason to believe there is something wrong with my computer, so I am puzzled and annoyed.

Edit: I have 8 GB ram.
Edit2: Turning off "start-on-access" (AVAST antivirus) have little effect, idle time after copying/moving seem to be almost 20 seconds.

There's lot's of complicated reasons for the differences in copying - and, frankly, I don't understand many of them!

I've used the free TeraCopy for copying at times. It seems to work faster than the built in Vista tools.

I will check out this TeraCopy, thanks.

I use TeraCopy and copying speed has increased