This wouldn't necessarily have to be a web app. If you are talking "web" then it could be any monetized site. This could be a blog, informational site, simple

This wouldn't necessarily have to be a web app. If you are talking "web" then it could be any monetized site. This could be a blog, informational site, simple ecommerce or even a collection of a number of each of the above to combine for the amount that you are looking at. Of course, you are likely going to have a smaller upside with a blog than you would with a web app. In other words, TechCrunch (a blog running on Wordpress) is a successful tech news site but it doesn't have the same potential as Facebook. I don't see why there would have to be a high failure rate for web apps which might bring in 1 - 2K per month. That's a business and as long as it's paying for it's cost and your time then there would be no reason for it to fail other than flagging interest of the owner. That range for two developers with no other income would be a problem, but for someone who spends a few hours a week on the app and has a day job, then it might be a nice income boost.