A peeved tech
The amount of time that antibodies last after a vaccine is given varies from dog to dog. Some may well have immunity for the rest of their lives, while others may only have it for a few years. The problem is, doing titre tests is much more expensive than the actual vaccine itself, which is why we recommend a three year rotation because that is the minimum it is guaranteed to last. We do have some clients that elect to do the blood test instead, and we usually push for it if the dog has health problems that we don't want to exacerbate by vaccinating. However, it is incorrect to say that all dogs have lifelong immunity after their initial puppy set, because that is simply not the case. Only just recently did we run a titre on a dog that was due for it's vaccine (I'm unsure if it was parvo or distemper) and they came back with an insufficient reaction. If you've ever worked in an isolation ward full of parvo pups, you'd make sure that your pet's immunity was sufficient to ward it off. To top it off I think it is also outright negligent to not vaccinate your pet for rabies. 55,000 people die from rabies every year (mostly in Africa and Asia) and the main source is dog bites. One of the main reasons it's so rare for people to get infected in North America and Europe is because of widespread vaccination of pets. Vaccinating your pet for rabies not only protects your pet, but also your family and community as a whole.
And finally, vets and techs are pet owners too. We practice what we preach. Any self respecting vet wouldn't do or recommend anything they wouldn't do for their own animals.