Bitcoin needed maximum 'memeability' i.e. the idea had to spread as fast and wide as possible. That is why the 4 year halfing cycle and absolute scarcity was chosen. The 21 million cap is easy to understand and tell your friends about. The possibility of getting rich is the strongest meme.
You really need to get someone rich in order for the meme to spread. This is the only way. People have a natural tendency to not be interested in currencies. Thinking about currencies makes their head ache. It needs to be really rewarding. On the other hand, there was no precedent and it was really risky. Most people were throwing away bitcoin at the start, and they just wanted it to spread.
In Bitcoin the security depends on the price of the currency. If the price doesn't pick up, the network won't be secure enough. It has to be rewarding, it has to spread as an idea, it has to be secure. The more secure it is, the more plausible it is to succeed, and so forth.
Most people don't really understand the disinflationary model as you explained, although I agree that in theory it is better and more elegant way to distribute coins. However, I think that if Bitcoin had chosen this model, it wouldn't have taken off. This model has too high inflation for too long, and the meme and security would have died off.
If the inflation is too high for too long, the meme won't spread, and the price will stay very low or nearly zero. Then a single miner will mine all coins and no one buys them, or only a single rich dude buys them. So in the end the coins won't get distributed as widely / fairly and the project will fail.
I think that Bitcoin succeeded in it's distribution as fairly as possible. I don't think that this can be replicated. It's impossible to create a new cryptocurrency where someone won't scoop them all off cheaply in the start, and that's why the creators typically own most of the coins, which will eventually doom the project. The infinite disinflationary model might be the only way to succeed in distributing a completely new currency, because no one wants to invest in it. But it has to have some other properties in order to spread widely.