I'll be very interested on what Jon has to say on this when he has time.
This is not just happening on x-cart. I manage 4 other WordPress sites and I'm see this on them as well. I assumed that Google is now doing a better job of checking old links. What I don't know is if the old links are just in Google's database or if they are external links from other sites. Because they may be links from other sites I always use a 301 redirect to a new page so I don't miss out on any possible link juice. This is why I mentioned Jon's new module in my post above.
Now to wait for Jon's response
