The problem with titers is that there simply isn't enough data yet to really know when they are protective. There have been horses with negative titers that didn't get sick and others with high titers that did. The science just isn't there to back up using titers in horses at this point especially when the vaccines are effective and have such tiny risk of serious adverse events.
My horses get EEE (Eastern Equine Encephalitis), WEE, VEE (because we are down here in Texas), WNV, and Tetanus in the spring. In the fall I give Influenza, EHV (Rhino) and Rabies. The timing on the Rabies is because that is when I have my coggins tests and teeth floating done.
What everyone needs to realize is that while there is a core set of vaccines that all horses should get at least once a year (recommended in the spring prior to biting insect season), the rest of the recommendations are based upon age, use, geographic location, and other factors. There is no one-size-fiits-all program so you can't compare your vaccination program to someone else's and say "oh, I don't need x" or "I must need to give y". The core vaccinations are: EEE, WEE, WNV, Tetanus and Rabies. All horses should get these and this is as far as you can go with comparing one vaccination plan to another. But someone else may live in an area where they actually recommend EEE, WEE and WNV twice a year rather than once. Or if your horse shows or lives in a barn where horses travell, besides those core vaccinations your vet may recommend Influenza and EHV (Rhino) as many as 4 times a year.