Zeroing out counters

Yesterday project manager on my project asked me about what would happen if count of registered users on our production website would go over 10,000. Now we have something aroung 8900 users and she is wondering is our database counter would be zeroed if more users would register.

It was an obvious awe on my face, but I answered that we can have almost undefinite number of users in our database.

I wonder why somebody who is working with somebody who has more that 14 years of experience building various databases (me ;o)) would be evere concerned about that kind of topic?