If TrailRunner was ShareWare you would actually buy something from me, meaning we both would have a contract and would bind us to a license-agreement. This would also have implications on what you’d expect from me, based on what you are accustomed with when you buy regular commercial products. So distributing TrailRunner as a ShareWare would require me to give you some contractual guarantees, which I can't. So I am not trying to play the big guy where I am small.
For all these reasons, TrailRunner is donation-ware (wikipedia explanation) or support-me-if-you-like-ware, even with a fixed amount. I think the amount for the token of esteem is really worth it. But if it's too much for you, just continue to use TrailRunner as there is no functional limitation for unregistered users. (Though TrailRunner won't hesitate to increasingly appeal to your honor)
That's my point of view regarding fairness. If you find this unfair, please drop me a line.