Vista and Activation

A week or two ago I decided to take a Lacie mobile external usb drive and reformat it to use as backup for my Macbook Bootcamp Vista partition.  I booted into Vista, connected the drive, and using the built in features in Vista, reformated the connected USB drive to NTFS.  Upon completion of the formatting, a notice popped up on my screen stating that my hardware had changed and Vista needed to be activated.

I ignored this, unplugged the USB drive and rebooted.  For a number of days saw nothing related to the reactivation until the other day.  Again I got the notice to activate Windows.  So I tried.  It did not work.  So I had to call India, I mean Microsoft, and walk through an automated voice response system with no success and finally a person.  It is strange as it involves the user to enter or speak 8-9 4 digit codes.  I had to do this 4 times in order to finally complete the process and get the new code to activate.  The Microsoft person also asked me a couple of times how many computers this version of Vista was installed on.  I guess the first time I told her only "1" was not good enough.

But what bothers me the most was why by reformatting an external USB drive cause this????