IMHO it is better to err on the side of under- rather than over-fertilizing, at least for apples, as overfertilizing (esp. too much N) gives you a bumper crop of watersprouts, which are a giant pain in the butt.
Whether you need to fertilize at all depends on your soil, IMO. If it is very sandy or low-fertility, maybe you do; but in decent soil you should be able to go some fair number of years without necessarily needing to do anything.
If you are getting small, inferior apples and the tree looks unhealthy, I have had good results with the fertilizer spikes (that you hammer into the ground around the dripline). I got huge apples that year.
On two other trees, I butchered chickens under them one year and let the blood drain on the ground (and watered it down afterward) and got the nicest apples the following year.
I think if you know you've got poor soil and the tree shows it, then it definitely helps to give it a little something extra.
I know our soil isn't the best, and just gave our trees a big heaping side dressing of broken down horse manure, then covered that in mulch. They seem to be really grateful for it too this year! (I did not do this to the trees we JUST planted in the fall and spring, only the 2008 plantings.)
Other then that I would have left them alone. I don't think I will buy into the 'fruit fertilizers' they have the store.
I also took a look at the organic fruit tree bugs sprays (dormant sprays) read the bottles... most of them now are all just Neem oil by 70%, you can buy 70% Neem oil cheaper then buy the 'fruit tree' sprays which are the same. Just different labels.
Yeah, i think i'll stick with maybe adding in compost or organic matter worked around the trees. I'm looking to plant a few fruit trees this year so i'll just plant those this year then next year with compost/ broken manure.
It also saves money to not buy the fruit fertilizers they have at the store.