Put a sustainable pricing model in place that can afford support staff.
Sure, a bunch of cheapskates will up and leave - there will surely be a second rate competitor who will pick them up and offer the same poor or nonexistent support all over again.
One thing I learned from experience is that it's the people who pay the least who are the neediest and most frustrating to deal with.
As someone who has partaken in a support organization where 99% were annual payments and 1% were "golden licenses" (pay once, never again), I can confirm that the 1% were by far the worst.
And even if it's not technically a service, but say some closed source software or whatever, the same idea still applies for future bug fixes and maintenance, at least in my mind. At least for anything semi-critical.
That said, support as a subscription (or alternatively, pay-per-issue) is totally fine by me. I'm also fine if new features are added to Version 2, and I later have to decide whether to upgrade or not.
And although it is not about the money for me, it frequently does pay off. I usually opt for the longest recurring subscription (if lifetime is not available) which usually has steep discounts and in the case of my XM radio... still enjoying that lifetime subscription.