It is more work to have personal defaultts rather than a global one and if Max doesn't choose to spend his time doing that, I won't complain.

Any webmaster will want to set such defaults to what, in their judgement, is most convenient for most people. If you have large number of threads then displaying 3 days is not desirable; on the other hand if there are few threads 1 day doesn't show enough. It is a matter of judgement and it is perfectly reasonable to revisit it from time to time to change the defaults to those you think are most appropriate.