I would be more inclined to think that whoever registered it, actually
does so he can get those misdirected emails; my suspicion was confirmed
after seeing this on
http://www.invalid.com:
===
Hi everybody,
Thank you for all the e-mails you sent to us! I promise to read them as
soon as I can, but please be patient - today there are 292,988 unread
messages in our invalid.com inboxes and I'm all alone at the office.
Maybe you want to buy my domain name and get a couple of thousand
e-mails every month? It's a lot of fun, but I guess you too would feel a
bit exhausted after a while
Take care!
Elsa W.
(e-mail address removed)
===
Seeing that, I cannot bring myself to think it's impolite to use it as
/dev/null service (it's still impolite to your reader though). I'm a bit
suspicious of their real motives though, who knows if it's owned by spam
email address collector.
example.com, though, seems to be registered to IANA (Internet Assigned
Numbers Authority).