The GoDaddy PR department released this comment:
"Go Daddy monitors DNS queries to ensure our customers' information is being accessed properly and not being harvested for unintended uses.
If we suspect that any service is gathering DNS data, we will limit access to that specific source. This is done to maintain our high level of system integrity.
If a company or service has questions about accessing Go Daddy DNS, they can email firstname.lastname@example.org.
Director, Domain Services"
It's nearly identical to the comment they made on WHOIS blocking earlier this year (see domainnamewire.com/2011/01/04/go-daddy-explains-whois-blocking/ ).
Of course, losing WHOIS access is just a minor inconvenience for most people, whereas the Internet would not function without DNS. And with WHOIS, most GoDaddy customers don't care (in fact, would prefer) if the access is blocked. But I'll bet very few, if any, GoDaddy customers would prefer to have DNS blocked!
It's starting to sound like this comes close to a network neutrality issue.