It's great to see that a book that inspires me in the world of business really does work. The guys at 37Signals aren't just all talk, they provide ideas that actually work as we can see. Thanks for the post!
You should read both, "Getting Real" is more focus on starting
the project and getting the project done, Rework has some of that but it's more about efficiently running your business and marketing it. These book and the one by http://www.softwarebyrob.com/ are the best business books for startups, after that just get to work on code and design.
Nobody cares how hard things are to code except for people are are already naturally disinclined to pay for software. Difficulty of execution may, for a very large swath of possible apps, be inversely correlated with success.
FWIW: The answer is "yes", followed (implicitly, because you didn't ask this) by "yes, people did pay", followed by (to the question you actually asked) "reread the article".
$25 is not that much; the secret is in making customers believe it's worth it, i.e. good marketing.
People pay a minimum of 1000 USD for an Apple laptop. I work on a 500 USD laptop from Asus, which I believe is just as good. But it's not as cool and people don't envy me :)