They most definitely have the right reasons for why someone should pay what they're asking. The reason #1, "we need to make a profit", is the biggest reason for the price. In reason #4 they clarify that reason by having tested that out of $10, $20 and $100 prices they made the biggest profit with the highest price.
The flimflam about updating the app just means that they don't wish to fire everyone now that they have a selling app, but instead will keep developing it with the hopes that it would sell even better.
The right customers -- professional developers -- would want the tool to stick around for a while, but of course there is a free-loader problem.
Paying $100 a year, let alone $100 once off, for something that improves productivity ought to be below the level of even caring to do the cost-benefit analysis.
If your employer won't let you spend $100 on a productivity tool, he's very foolish. (NB: Most employers are foolish. I've always got hemming and hawing about spending that money; can't we just do without?)
The flimflam about updating the app just means that they don't wish to fire everyone now that they have a selling app, but instead will keep developing it with the hopes that it would sell even better.