If I were Satoshi... I would have built a modest amount of inflation in to bitcoin. "Modest inflation is what most people are comfortable and familiar with," I would have reasoned to myself, "so that's the right thing to do."
However... I'm not so sure that would have worked. It is very nice to be able to say "bitcoins are valuable because they are rare, and they are rare because they are designed that way-- there will never be more than 21-million of them." That is easy to understand, and gives bitcoins a clear advantage over existing currencies.