Generally speaking, don't most users prefer one-shot payments, even if it is a relatively large amount, rather than monthly subscriptions? So it doesn't require followup mental maintenance... You just pay once and forget.
I was thinking the same way, but once a client explained that at least for them it is the same - they periodically roll out the major version update which is paid, and users pay upfront a lump sum the amount they had to pay anyway if it was a monthly subscription during that period.
