Thank you. I'll be the first to admit we had a rough start with BillMinder but we've done our best to improve it (and will continue to do so) and had some major updates and as well as a few minor ones. We generally try to put out simple applications that WE would want to use and let our user base help us decide what else is needed (suggestions always welcome -- we can't always implement them all, but we do take them all seriously and consider them).
I'm not defending the maker of said ToDo app but I can tell you from experience that once an app is off a Top 20 list in its category, it only sells 5-10 copies per day (at best). At 1-3 bucks a unit, this makes for a loss of money after one puts in time answering support emails and basic maintenance. It's sort of unfortunate, really, as it's very easy for an app to get entirely lost on the App Store and literally cost one money to maintain since there is little to no return on the time investment. That developer probably moved on to another application or gave up entirely. It's tough to justify the time when you're putting in 20-50 hours a week and getting a couple hundred bucks a month of out it. Granted, few people do that. I don't mean to sound greedy in saying that. The fact is most developers on the app store aren't making 5k+ per month, 10k+ per month or the elusive 10k/day in the top 10..it's more like a few hundred dollars a month or perhaps a (very) few thousand a month if you happened to come out with a popular product.
Anyway, have a good one!