His sales of RocSim may also might be a factor of how much time he puts into development.
With several FREE software packages out there, if he isn't selling enough, he might see more development a waste of time for free upgrades to already sold copies
As an entrepreneur I can tell you that it is in fact the opposite of what you're suggesting, that is if you are on the other side of the curve. It is fairly common for a company to invest in developing a product, take it to market, gain popularity and market share, then just ride the wave. If the product is something like software and there is a sustainable market for that product, and if the owners of the product investment in regular development, then all things being equal, it should remain ahead of the freeware offerings.
I have no idea on what Tim's sales are or even what the realities of that market are, but I am an owner of RockSim and I would have actually invested in RockSim Pro at some point had it been an option for a non-US citizen, but it is not. Having said that, if it was an option at this stage I would not invest in it or even the basic version simply due to the obvious lack of development. If the market was there then I believe that if Tim revisited his price point on the Pro version as well as developed another price model such as the SAS model (Software As a Service), and committed regularly in development, then he would increase his bottom line.
But at this stage the volunteer developers of OR have done a darn good job in closing that gap, so now Tim is faced with being reactive. It is like the plane flying analogy where it proportionally takes more effort and resources to take off and climb to 30,000', than to simply cruise at 30,000'.