Outlook and compressing data file size

I'm using Outlook 2003 possibly 2007.

I've run the compact data file command on the various personal folders including the outlook data file.  It is taking a while to run which would indicate that it is compressing nicely and I see the file sizes falling substantially.

My question is why this command is not run periodically in the background automatically  by Outlook.  FOr those not technically minded, surely their data file size will just incrementally increase without being reduced in size.

Also is a 2 gig outlook data file too large and suseptable to corruption?

Finally with respect to the auto archive options, what is the purpose of this when I manually move emails over 1 year into a sub-folder or different personal folder? Does auto archive risk deletion of emails over x period of time?