Discover Card "Enhanced Sercurity"

A week or so ago, I logged into my Discover Card account and had the following message:

“A Discover Card with a new account number has been mailed to you as a replacement to the card you currently carry. Your account number has changed as part of a systems upgrade that offers you even more
benefits, such as, enhanced security monitoring on your account to help detect fraud earlier.”

I then received a new Discover Card in the mail.  When I called to activate, I asked them why one 16-digit account number is more secure than another one.  The CSR claimed that in November 2007, they did a system update to “better manage” my account to give me “the quality of service” that I deserved.  I then asked them why they couldn’t do that with my old account number.  The CSR seemed a little dumbfounded.  He then said that it was because the way the old accounts were numbered, they couldn’t do that.

This seems funny to me.  It seems like Discover Card / Discover Bank had some kind of security breach and they aren’t telling their customers.  This is enough for me, however, to take Discover from being my primary personal credit card to an emergency one that I keep at home, at least until I get a satisfactory answer.

What do you guys think?  Am I blowing this out of proportion?  Does it seem like Discover is hiding something?