The key thing to note is that anti-poisoning countermeasures deployed at major authority servers scale to provide value without incurring cost for every (serverside) Internet "user", and DNSSEC doesn't. A lot of these thing seem like (really, are) half-measures, but their cost/benefit ratio is drastically different, which is why they get rolled out so quickly compared to DNSSEC, which is more akin to a forklift upgrade.