It is but time has a big impact on batteries too. That is why your 1000 cycles "guarantee" only applies within the 3 year applecare period. After that it is considered a consumable item and it is your responsibility to pay for any replacements.
Basically your battery will begin to die badly sometime between 4 and 6 years of age there is very little you can do about it and it seems to be luck of the draw wether you get a long or not so long lasting one. Although they do seem to be getting better as the years go by.