How about his:
Remember the two variables:
Bitcoin Price and
Bitcoin Difficulty, buying a contract you counting on the bitcoin price will rise the same or more as the bitcoin mining difficulty.
This Difficulty rise can overtake the bitcoin-price growth overtime.
Is this more clear?
If you decide between mining and holding, you need to calculate in Bitcoins, not dollars. So if you invest 1 Bitcoin, days-to-ROI is when you recover this 1 Bitcoin back. The price is only relevant when you calculate maintenance costs.
Roger, I think you're missing the point entirely of what
ZetaOS is trying to say.
He's not advising against buying mining contracts, he's saying that when buying contracts, consider both the ROI rewards (i.e. the cost of the contract vs the time it will take for you to get your investment back)
and the difficulty factor (i.e. the time it will take to hash a block and earn a reward). I dare say all ROI calculators base their results on current hash-rates and difficulty for them, they can't predict where the hash difficulty of any coin will be two years from now, because you can't predict how much hash-power will be invested in any single mining effort or whether that hash-power gets reassigned to other less difficult and more 'profitable' coins.
At some point, the difficulty in Bitcoin mining will be such that even at 10k$ a coin, it will no longer be profitable to mine anymore because the difficulty has risen to the point that it then causes any future earnings to be entirely consumed by the liabilities (service & maintenance fees) expended to mine the coin.
There is nothing inherently contradictory in both holding Bitcoin as a long-term investment (in the hopes that the price will continue to rise) and mining it (which only serves to increase your holdings in that investment).