I think it's more interesting than you make it out to be. Consider the fact that if you try to reorg the entire blockchain, you have 100% chance to eventually succeed, no matter how low your hashrate (assuming that the ratio between your hashrate and the network's has a positive lower bound).
Indeed, while I was well aware of growth making the historical hashing inconsequential (
http://bitcoin.sipa.be/powdays-50k.png) and playing the reorg lottery I hadn't considered that particular possibility before reading that paper (thanks for the link). Though it does require also exponential growth, which is physically senseless in some sufficiently long run. It would probably be interesting to explore the probability distribution with a relaxed form of that assumption.
That's the beauty of it - the result doesn't require exponential growth (though it does help a bit). If the hashrate of attacker and network is fixed to eternity, the attacker still has a chance of 100% to succeed eventually. This is because the harmonic integral diverges (the cumulative PoW increases linearly, so his probability of success each day decreases inversely linearly. The sum of this goes to infinity and this can be translated to 100% probability of success).
A positive lower bound on the hashrate ratio is a sufficient (though not strictly necessary) condition for this guarantee.
