I think one of the most important things to consider is: Why do these people have BTC in the first place? Even though purchases are made through the currency, it doesn't mean that every single BTC user is looking to buy things with it. A lot of people are just holding for something better on the horizon. Like mentioned earlier, grab the market size for customers actually wanting to purchase an android box (me as a matter of fact, but just have to bring myself round to actually buy one) and cross-check that against customers who actually have an incentive to buy through BTC (as for me I would rather pay through credit/debit card because it is a much simpler route to get funds from A to B. BTC funds probably won't cover it unless buying more atm).