This is exactly what I've been asking. This means that the exchange is using relative values (percentages) in calculating the bonus. In fact, I think you are confusing something since if you, for example, deposited 1 BTC, got 0.01 BTC as a bonus, earned through trading 8.99 BTC (so your total is 10 BTC), and then decided to withdraw the funds, they would deduct 0.1 BTC (1% of 10 BTC), which is nonsense...
If what you say is nevertheless true, such marketing tactics would be a masochistic exercise in stupidity
Firstly you are guaranteed that you will lose some money whatever if you got any profit from trading there or not.
So this tactic is smart from them but for users it not good because it's not good, we are not fools.
This tactic is not smart. I'd argue it is pretty much stupid, since traders are not fools and would stay miles away from such an exchange (that would allegedly grab some of their hard-earned profits). In fact, I've never heard about any exchange using something similar before. Could you please post a link where this bonus accruement on deposit and subtraction on withdrawal is described in greater detail (preferably at Bter itself)?