it means that users can't accidentally not use Tor
Not strictly true. The authorities in a country where Tor is needed to get free access to information could arrange for fake DNS responses to be returned for .onion sites, maybe even routing the requests through a proxy server onto the Tor network so that people might not notice immediately that they had forgotten to switch to Tor. That way, they could easily catch a few users and possibly discover hidden services that may be "of interest" such as sites used to coordinate protests.
This is, in fact, how Tor transparent proxies, used to "torify" an entire network, work. A simple setup will return the IP of the proxy server for all .onion addresses, then extract the required "domain" (.onion address) from the HTTP request, while a more complex setup will return a dynamically-assigned IP address from a large pool for each different .onion address that is requested, with the proxy server, answering on all addresses in that pool via NAT, using either a reverse lookup or some kind of direct IPC with the nameserver to map it back to a "domain".