There's also a flaw in this logic: It assumes that all apps require some kind of server provided by the developer in order to run.
Once upon a time, standalone software was standalone and could run in perpetuity without requiring anything more of the original developer. It's still entirely possible to write software like this, there's just a trend away from it due to the prevalence of always-on internet connections and the ease of keeping some of your application server-side as a form of copy protection.
“Thanks for contacting us! Our standard license includes support for 12 months after purchase. I’ve attached an offer for our extended support contract. I’m looking forward to your response!”
The extent at which some users subsidize the app for others is just one of the decisions you need to make when deciding on a pricing structure, not a rebuttal.
However, that is not the case. Everyone stops using your app at some point. So you don't need to support users forever, you just need to support them for some finite amount of time. Some users might use your app for a few years, some use your app just for a few weeks. Some users will email you half a dozen times, but most will never email you. Your app price should be priced so you can afford to support the average user.
And another thing that people forget: When your user base is growing, the amount of word of mouth recommendation you get also grows, and you automatically start selling more licenses, so your revenue also grows.
Pay-once and subscription aren't really that different in practice. Pay-once even has an advantage: You get all the money up front. And that's awesome if you are planning to grow your company.