My workaround for this was to add a TXT record for *.mydomain.com that just returns a string like "Unused". This seems to stop them from hijacking any subdomains, and it's not an A record so undefined subdomain names do not resolve, just like if you had not defined them in the first place.
(Workaround shouldn't be necessary of course, but this kind of bullshit is par for the course with cheap hosting companies.)
example.com isn't just better: it's actually specified in RFC 2606 as one of the domains "reserved for use in private testing, as examples in documentation, and the like."
While it is probably not relevant for must users, there is a subtle difference between "There exists no A record for x.example.com" and "There is no x.example.com".
A workaround for this is to make *.example.com a CNAME for something.invalid. ".invalid" is a reserved TLD guaranteed not to exist so this should force all queries for non-existent domains to come back with NXDOMAIN.
I'm with gandi, there's a few things I don't like but overall they've been super stable with very little headaches. I think in the 3+ years I've been with them I've had one slight issue that was dealt with in <24 hours.
I typically just do a *.example.com @A record to the IP address, works just as well and would fix the specific problem in the link (unless he's worried about having to extract individual subdomains to go separate places later).
(Workaround shouldn't be necessary of course, but this kind of bullshit is par for the course with cheap hosting companies.)