Online Mining Calculators using prebuilt machines data I've read many comments that mining is not profitable, or barely.

Using the machines' data at Hardware Comparison in online mining calculators do show some with good profits. Am I missing something or misunderstanding the data? I only used the Mhash/s, watts, and price.
The problem is that the difficulty rating is going up, and going up significantly.  This happens for two reasons.  First, the number of mining rigs increases as people try to get involved with Bitcoin mining.  Second, ASIC-based miners which can run over 60GH/s using around 600W are just arriving in the market and once more generally available will cause a big leap in the difficulty.