Earlier quoted context omitted.
How is this necessary if there is a grace period after a domain expires?
You can't use your domain in grace period until you pay. It gets redirected.
DENIC, for example, (which operates seperately and has their own, incompatible WHOIS system), operates .de differently:
After your domain ran out, it will get "locked", all DNS settings will be locked they were before, and you get a letter or an SMS. The domain will stay locked for 2 weeks, during that you can enter the code from the SMS or letter on a website to move the domain to another registrar or delete the domain.
If you don’t react at all, after 2 weeks, the domain goes into TRANSIT. It still stays locked, but now you get actually billed for it, until you enter the code or delete the domain.
Essentially, with DENIC, the domain stays locked until you decide to delete it or move it to another registrar.
You can also disable the TRANSIT, in that case, if the domain runs out, after 2 weeks grace period of being locked it actually runs out.
Remember: Not all NICs operate like ICANN.