Quck update: Coinbase no longer seems tied to Bitstamp, at least not this very moment. Both the buy and sell prices are above Bitstamp's. They're either making a hard buy themselves, or are tracking to another system. Any ideas?
Will try to back my findings up with new charts, soon.
I just started to notice this the other day as well. I figured since they were a BTC/USD exchange they would just establish a market rate themselves. The only thing I don't like about coinbase is you can't put in reserve buy/sell orders at a given market price. Meh, other than that I like coinbase a lot, very stable and reliable.
They likely use a number of exchanges and probably keep some for their own investment without even using an exchange at all.
For example if one person wants to buy one bitcoin they can sell it to them for $600 (they would already own it). Then if someone wanted to sell a bitcoin they could buy it from them for $589 to replenish their supply. Then they can adjust their prices based on a number of exchanges and based on how much people are buying and selling.
