Hole in Bottom of Beer Stein?

I was looking at a nice old pewter lidded stoneware beer stein from Germany
in a local store, but the bottom of the stein has a hole in the bottom of it
where it looks like a glass sleeve/cup insert rests so that you can actually
drink out of it. However, there's no cup/insert in it. Would this lower the
value of it, and why would the stein be made this way? The stein displays
very nicely, since you can't see the hole in the bottom when it's sitting on
a table.