I didn't want to raise this issue while the game was still new and relatively visible on the XBLCG service, but it's something I'll discuss now that the game has been out for a while and I've had a good chance to analyse the results.
One of the questions I've been asked about Time Flows, But Does Not Return is why anyone would pay for a game that could be completed in under 10 minutes, especially since there was no difference between the trial version and the purchased version. Part of it was simply that the game felt "done" in the form it's currently in. There was more content at one point while I was working on it, but ultimately it felt like anything beyond what's in the game now was superfluous. The game takes 6-8 minutes to play because the experience that I was going for took me 6-8 minutes to communicate. I was concerned with getting my ideas across as well as I could, and I wasn't really thinking about the trial time limit while I was creating it.
Towards the end of the process, though, I had to decide if I wanted to deliberately limit the demo in some way, knowing that I could release the full thing essentially as a free trial. I chose not to primarily because I never viewed this as a commercial product; it has always been about communication and experimentation for me.
So the question then becomes, why should anyone pay for it, since a paid version is available. The main reason is because I was hoping that players would question what exactly it is that they pay for when they buy a game. Why do you pay $2, $20, or $60 for a game? Is it because that's how you unlock "additional content", or is it because you gain something valuable out of someone else's work and you want to support what they do? This was my way of seeing if people were in fact willing to pay for something entirely to show their appreciation for it.
The result of this experiment was pretty positive - more than enough people have bought the game to cover the meagre costs I incurred making it. The conversion rate (how many people buy a game v.s. how many people download a trial) has also actually been pretty good - a bit below 2%. That might not sound very good, but 2% is considered to be pretty decent for most downloadable titles. I think it's even better given that - unlike other downloadable games - a purchase provided no additional content, and I made no attempt to "upsell" or advertise within the game, aside from providing a menu option to buy the game (the screen that appears after the 8-minute demo timer expires comes from Microsoft, not me).
As for people who didn't pay for the game, the most common thing I heard was that people didn't buy it precisely because they expected to get something extra in return for paying. That might not be so good for me and this particular game, but I think it bodes well for the service as a whole. Xbox Live is known primarily as a place where bigoted, immature young men gather, but I've learned that there's actually a pretty sizeable portion of the market made up of people who are looking for more risky, thoughtful works. And I think that's fantastic, even if I'm not the one who benefits from it.