Yearly blood panels provide time series data against which it might be easier to spot changes even if all metrics are in the "healthy" zone.
At Kaiser, which usually has its own lab in every facility, yearly blood panels are completely routine. As an HMO Kaiser has every incentive to minimize costs, and they don't make any such practices routine unless and until they've been demonstrated to provide clear benefit across their patient population. (They also regularly run all sorts of trials--they're vertically integrated from the research lab on up.)
Kaisers / HMOs are not that unique in having annual blood work of standard items. I think they have to do it by law at some level, with PPO insurance 'preventive' stuff like that is usually much cheaper or 'free'.
