There are a lot of problems with this argument, especially when you go into the ports section. For example, the version of go between 5.4, 5.5, and 5.6 is different for all three versions, which means you're going to have to rebuild packages, run regression tests, etc every six months to make sure some new feature doesn't run into your code, or some bug isn't introduced. Similarly, in the case of the base install, you are still going to have to run a regression test there to ensure that any deprecated or removed features don't impact your workflow.
These things are expensive from a development and ops perspective, and why most commercial software vendors tend to stick to a releasing for a few platforms they know are going to be supported for longer than a year or two. Yes, OpenBSD upgrades are mostly painless, but still, bugs can and do happen, and expecting everyone to be able to just drop everything and rebuild is plain and simple unreasonable.
These things are expensive from a development and ops perspective, and why most commercial software vendors tend to stick to a releasing for a few platforms they know are going to be supported for longer than a year or two. Yes, OpenBSD upgrades are mostly painless, but still, bugs can and do happen, and expecting everyone to be able to just drop everything and rebuild is plain and simple unreasonable.