If a developer redesigns and rewrites an application why are they not entitled to make their users pay for it again? You could just keep using the old version.

If a developer redesigns and rewrites an application why are they not entitled to make their users pay for it again? You could just keep using the old version. I think it's absurd that people complain about iOS apps being "yet another $5" given the amount of time it takes to make a beautiful application. Given that iOS developers have no ability to offer upgrade discounts, I fully support them charging full price for new versions. They deserve it, especially given the hundreds of dollars people pay for new versions of Office, Creative Suite, etc each year.