I do not expect software pricing to match the marginal cost to the supplier per se. And you're right that pricing in general is done in relation to what's the customers perceived value.
However, I disagree with your first statement. Lets take Highrise pricing plan as an example. For the 6 user plan you pay $24/month - which comes down to $4 per user. For the 15 user plan you pay $49 - about $3.26 per user. So my total cost of course goes up with usage, but not in a linear fashion.
You could also make that happen with the $x/user/month scenario, but that gets probably rather complex without ending up with tiers again.
However, I disagree with your first statement. Lets take Highrise pricing plan as an example. For the 6 user plan you pay $24/month - which comes down to $4 per user. For the 15 user plan you pay $49 - about $3.26 per user. So my total cost of course goes up with usage, but not in a linear fashion.
You could also make that happen with the $x/user/month scenario, but that gets probably rather complex without ending up with tiers again.