Why do dustcoin.com and coinwarz.com give opposite results of profitability? It's been several days in a row that I go to dustcoin and see Dogecoin being listed as less profitable than either Digitalcoin and BBQcoin, with the latest being the most profitable.

But then if I go to coinwarz I see the inverse: Dogecoin is the most profitable, next Digital and finally BBQ.

The prices listed for them are not that different, nor is the difficulty - below the values. E.g. the values at the time of writing this question - first columns are from coinwarz and then the values for dustcoin:

coin   vs. BTC                diff.    vs. BTC   diff.
BBQ  0.000048 (Cryptsy)      4.3986 0.00005165   3.192
DGC  0.00036494 (Cryptsy)   11.3679 0.00035000   8.062
DOGE 0.00000031 (Coins-E)  286.6240 0.00000028 271.845


I would've thought that getting the profitability would be a straight away calculation, given the hashpower at your disposal vs. the avg. reward for a coin, plus the difficulty of it's network and the value it commands on the market.

So I can't explain why each site gives the exact opposite answer for these coins in particular - my inner cynic suggests at least one of them gets paid to artificially increase/decrease the profitability of some coins, but I find that hard to accept as well.

Any ideas?
First off, don't listen to so called "profitability" calculates they are always wrong.

and here's why:
Each "profitability" site bases the profitability based on the current block on that network vs bitcoins current block. Well most of these coins have a limited exchange volume on exchanges (some as low as 0.001 btc) yet because of that activity they are deemed to be more valuable. What happens next is a huge dump of coins and a market crash. This leads to an increase in diff and a decrease in profitability. Using that theory, you can see that these sites are not going to be correct. Especially depending on the exchange they use and the rates they use. Most coins only convert from ALT->BTC. So that means they will take the BTC/USD price from somewhere like bitstamp and then take the ALT/BTC price from the exchange of choice and finally it will take BTC*USD.

BEGIN EDIT
Simple formula these sites use

$profitability = $USDperBitCoin * $BitCoinperAltCoin

END EDIT

tl;dr
Exchange rates and exchanges used.
Low volume of trade.
Unique Difficulty filter algos on unique coins

I suggest you ask the owners of the sites this one.