In the US, independent developers can charge,
- a 'purchase' fee
- a fee for a specific version, they hen pay a small amount to upgrade to the next version
- a monthly/yearly subscription (the Enterprise market is going in this direction, e.g. Office 365)
- occasionally, a usage fee based on the quantity of data used/viewed
I control the visibility of various options in the software through a licensing platform and charge a basic fee + whatever additional options they wish; works really well.
Hope this helps.
Henry