Ulrich is the most famous 'grinder' in that he pushes bigger gears at a lower cadence than say , for want of a better example , Lance Armstrong.
On paper and purely mathmatically its more efficient to sit in the saddle and push a gear of around 80 RPMs (ie Ulrich aka a 'diesel engine') than the faster cadence of Lance , at say 100 RPMs.
But in a race with the ebb and flow and fluctuating gradients and need to rest certain muscles , its clear the occasional 'honk' and higher cadence is superior.
Everyone has different muscle fibre aswell , and different cadences suit those different fibres.
Ulrich is known to have a higher density of slow twitch muscles , bad for sprinting but good for grinding - hence why he hasnt changed his style in 8 years.
He and his coaches obviously arent idiots , they'd have given the faster spin technique a try if they thought it was best for Jan.Armstrong obviously has different muscle fibres that suit this style.
There also must be some difference with lactic acid build up and breakdown.
If racing was about being wired up to a turbo trainer , Ulrich would probably be unbeatable , but its not.