They could probably still get wealthy by getting in on the action fairly early with a separate set of mining identities, if that's what they wanted.
A great deal of effort must have gone into staying anonymous, and planning & designing & developing the client, the network, the scripting language, the economic progression (difficulty levels, decreasing block rewards, etc) and even the ascii content embedded in the genesis block. There must have been a plan for the first mining operation as well, why put in so much effort and then be surprised it catches on?
The "unfairness" of pre-mining (or early mining) must have been considered.
OTOH i haven't looked at the numbers. Would a dump of Satoshi's holdings crash the market?
Had Satoshi used the coins before its time, it could have "contaminated" the experiment, and possibly crashed permanently the market. By mining and not using it, it increased its early value. I'm sure there's a mathematical proof somewhere that this would be the best option, especially if Satoshi is in fact a group of people.
Of course, Satoshi may still have the keys, and waiting a bit more before cashing in.
That's the beauty of bitcoin open ledger: we'll all know for sure in the next 10-15 years...
That being said, rather than a group of friends, a government agency or a highly secretive group of cyberpunks, I could imagine two or more family members keeping such a secret. However it would still be hard to resist the urge to cash in on even some of those mined coins, unless you were already stinking rich.
I know that many have theorised that Satoshi could have simply lost the coins, but as the author states in his article, it seems like Satoshi went out of his way to back up his clients on a regular basis. That isn't the action of someone who loses things so easily, especially if they both believed in, and could appreciate the impact of the project.
Just my two cents.