Say I was to buy a machine like this:

http://advancedminers.com/bitcoin-mining-hardware/1-2ths-bitcoin-miner/?gclid=CKjFyaOSnLsCFYl9OgodXFMASQ

If I am really mining at 1.2 TH/s then I am generating roughly 25BTC per month....

From this standpoint, it seems like a no brainer....the machine cost $6K, so I would make it up in one week of mining.....

Am I missing something?  I know the difficulty will be going up.....
And what happens in 2016?  BTC gets halved every 4 years?  What is that all about?


Any thoughts would be greatly appreciated.

Thanks,
RLF