Got to say congratulations on this but there is a certain amount of fortunate timing that's helped Trism be as popular as it is - mainly being in the store on day one (it was the first app I purchased on day one, as it happens.)
Unfortunately, for many of us, that wasn't possible. I'm in the UK and for a long time couldn't even apply for the dev program because it was limited to the US. Then, at some point before the app store launch, Apple changed this but didn't make it well known. I managed to apply a few weeks before the launch of the app store, just by checking to see if it has been opened up outside the US, but wasn't accepted until the day the app store went live. So I couldn't have got my game in the app store on day one.
Apps like Trism could leverage a huge amount of publicity, get great visibility in the app store, set a realistic price point for their efforts and reap the benefits of this. The situation is considerably different now - there isn't the visibility in the app store and prices are generally lower, especially from the small developers. For a small developer being in there at day one has basically built their brand and business and they'll continue to see the effects of that when they release something new - they already have a following.
That's not to say that it's impossible for small developers to match this in the future, it's just a lot more difficult as the app store gets more cluttered (especially with the way updates are posted), the larger development houses come along and pricing means that you have to shift an awful lot more volume.
I do like Trism (not as much as my wife, who loves it). It's a good game, even if the scoring in Infinitism is ridiculous