This is not a scenario where I think you can't do this just as easily, the idea is targeted more at those that don't have the skills that you do.
.io domain names cost around $80 (cheaper in some places) so the assumption is that $19 isn't really out of whack with what you might be willing to pay.
Also, as a developer you probably charge somewhere from $60-$120 per hour for your time. If it takes you longer than 15 mins to do this then you have just wasted money.
p.s. Thanks for being a little kinder with your edit :)
Perhaps, but I still think that $20 is a little steep. Especially since its just a list - it doesn't do much. $20 definitely is not an impulse buy for me. And you're welcome.
You also get the 4 and 5 letter word lists, but I thought that the scarcity of 70 might be more of a motivator.
One issue is that many people aren't looking for just any word, they want a specific thing. I wonder if the list should actually cost more and be targeted at domainers?
I think so, but you would need more features. I'm not inclined to purchase it, so I don't know how you're providing it (web interface, excel, txt, etc.).
If you want to raise the price and sell it to domainers, write an admin interface. Multiple TLD's and stuff. Have a feature which allows you to send them a notification when an unavailable TLD is expiring. Also, write a spider to check different registrars to find the lowest price for each TLD. Essentially, a SaS.
The time it would take to write a script in Python to go through each domain and check the availability would cost less than $20.
Edit: Here - this Python script generates a list of available .io domains of any length (user specified) in 9 lines. https://gist.github.com/4111298