One of the vases in HDTP has money in it (American Dollars) but in Deus Ex you use credits, not money like that, so why was that put in?

I remember that, and I remember asking about that, but I don't remember the answer.

It's like this -

You know when you go on holiday/vacation and you have some of the local currency still left in your pocket? You tend to stick in a drawer or, in this case - a vase.

Someone stuck it in a vase and forgot about it. Years later, dollars are no use because everyone is using credits - so it just remains forever at the bottom of that dusty old vase.