Not everyone using Bitcoin is concerned with anonymity, and those who are use Tor anyway, so their DNS queries are already anonymized. DNS query results get cached, too, so not every query is going to be visible to the person running the authoritative DNS server for the domain in question. Even without Tor, if you use a popular public DNS server like 8.8.8.8, 4.2.2.2, etc., then there's a fair chance your queries will be returned from that server's cache anyway. I don't see how this is any more of a threat than running a Bitcoin client without Tor.