I think there is a fundamental misunderstanding here, and you are missing the point. You can obviously buy at a higher price, but in normal exchanges (CEX/Cryptsy/etc), the order will complete at market price.

Consider a simple order book for buys (KS/LTC):

Total on sale: 120 KS total
seller 1: 0.07 10 (sell 10 KS at 0.07 LTC each)
seller 2: 0.08 10 (sell 10 KS at 0.08 LTC each)
seller 3: 0.1   100 (sell 100 KS at 0.1 LTC each)

Suppose I place an order for buying 5 KS at 1 LTC each (5 LTC total) (Here, I meant to type 0.1 LTC, but I made a mistake and typed 1 LTC). What happens?

In a normal exchange (CEX/Cryptsy/etc), the sale goes through at market price. I will get KS until all my LTC gets filled up. Since I placed an order for 5 LTC, I would eat up the first order (10 KS at 0.07 = 0.7 LTC); the second order (10 KS at 0.08 = 0.8 LTC), and part of the third order (35 KS at 0.1 = 3.5 LTC). Therefore, I would get 10+10+35 = 55 KS in return for my 5 LTC total.

In bit-mining.co, I would just get 5 KS for 5 LTC. The buyer spends 5 LTC, the seller (in this case, the top one) gets 0.07*5 = 0.35 LTC, and the rest (5-0.35=4.65LTC) is pocketed by bit-mining.co.

I hope this makes things clear.