Or it could just a a quirk of their database integer format... 
Most passive components like capacitors actually state their tolerance deviation and as stated above already, it's not a factor of voltage. While it is true that you might get longer "life" out of a higher voltage capacitor... since you aren't stressing it... it will still behave the same as a similar lower voltage unit. That is, unless you were stressing the lower voltage device beyond stated limits.
Sometimes though... tolerance deviations of up to 10% or more may not impact your circuit very much... such as a power supply filter. In tuned circuits like those in used in a radio perhaps... the value of a capacitor might need to be pretty close to the exact value printed on it and you would pay more to get the 1% to 5% tolerance version.