Note the question to which he had provided the answer.
His answer relates to
economic expansion first and foremost,
not just to bitcoin's divisibility (currently set to 8 decimal places).
Don't worry, I read the whole thing.
The fact of the matter is that this wasn't an answer that could satisfy the question of "economic expansion" aside from saying that it BTC is divisible enough to be used even if its USD price goes up to $1bn. This has absolutely no relation to an increased supply of BTC, rather, it responds to an idea that Gavin inferred from the "economic expansion" statement that the price of BTC would necessarily rise.
Can you honestly expect to see a more thorough answer made within 140 characters?