[stefanu]

You are right, it is not true of all proprietary software. There is no problem with software upgrades, not even with frequent software upgrades. Problem is when the software requires regular document upgrades. This requirement can not be met in real life, if you produce few documents a month.

[FollowSteph3]

What I'm saying is most proprietary software does offer document upgrades. You can open very old versions of Word, Excel, etc. My company supports opening backed up files up to about 8-9 years ago. The only reason we don't go further is that older versions don't work on modern OS'es and hence no one uses them. But even then it's still possible to upgrade if you really wanted to.