@Korb
It's not that you're missing something. That's a good assessment on the ROI and
the decision to buy or not to which I completely agree.
I was talking about people that
already pre-ordered and the race to start mining first and about people that would need to decide to keep the devices running once they will have them or buy more. And how difficulty and electricity price will influence all that.
Not everybody has 30k to buy a minirig. If I run your 100x difficulty example through the calculator at
http://bitcoinx.com/profit/index.php, with a 25 BTC reward, a 4.5 Gh/s Jalapeno and a 25W energy cost (jala + a netbook) I get all my profits eaten up by electricity.
Power cost per time frame: 2.74 USD
Revenue per time frame: 2.92 USD
... less power costs: 0.18 USD