When DNS servers couldn't locate the authoritative servers at Microsoft because of the misconfigured router, these servers began to expire their data. As time went on, more and more servers expired their Microsoft entries, which explains why connectivity problems to their site grew like the plague. It took time for DNS expirations to travel around. Expiration is a very important component of DNS because often no records are better than old records. If you've changed data and you want other servers to know about it, expiration can make it happen.
Many sites expire once per week.
Microsoft's expiration is high, which may be a reaction to another potential problem. Another key value to review is the TTL, which Microsoft configured for every two hours. TTL represents the time that a name server is allowed to cache data. Once the time expires, the server must get new data from the authoritative servers. A short TTL is useful because it keeps the information consistent but at the expense of performance on the network and server.