Would not leaving sufficient honey on the hive accomplish the same thing, or do you recommend actually putting feeders on regardless of the amount of honey left by the beekeeper for the bees' winter stores?
No....on both accounts. My comments are about having enough young bees as 1of6 commented. No matter how much honey you leave, or sometimes how much internal feeding you provide, it comes down to having enough young bees going into winter.
I have found that nothing beats external open feeding to simulate a flow, and stimulate the queen, into early brood or extending the fall brood season. The past few years here, we have had drought in July and August, inadequate flow in September, and early frost that kills off the nectar source.
What I am saying is you may need to analyze the local fall flow for northern areas, and augment feeding to ensure enough fall bees are raised. Waiting on the fall flow, or assuming that it will be enough on it's own, may not be enough.
This is why I use open feeding methods most of the time. A communal feeding station some distance from the beeyard, next to a primary nectar source, such as an orchard or garden, works well. Orchards and gardens are open sites for beeyards so the bees expect to harvest close by. Putting out a couple of feeders, even before that source comes on line, allows the bees to build stores without causing robbing as internal feeding can.
I feed the same way in the fall to help the bees build brood and stores for the winter.
The most important things in overwintering bees is not how much stores they have or the size of the cluster, both can be false indicators for the reason Bjornbee states. The most important factors are amount of young bees, availability of the stores to the cluster, and venting to control condensation.
A few things to consider:
If you have a small cluster of young bees in a large hive the stores on he outer edges of the hive may be too far from the cluster for the bees to retrieve if those stores are the only available during a cold snap. A Cluster that begins as mostly old bees with few young bees in ratio the old bees will often die during the winter and plug up the hive entrance and the young bees can't get out for sanitation flights and die inside the hive. A poorly vented hive can have the condensation rain inside the hive, if that rain falls on the bees and the temps drop sharply you've lost the outer layer of the cluster due to freezing.
I've overwinter bees in a 2 story 5 frame medium nuc, in the spring the cluster is no larger than a baseball, yet there is often 2-3 frames of stores (out of 10) left within the hive. Why? Because the space was small enough that the stores were close to the bees so that on warmer days they could go out from the cluster and mover the stores into cells within the cluster. No cell was too far away as may have been the case in a single 10 frame hive. A screened bottom board and a top entrance allows the moisture from the condensation to either vent out the top entrance or let the rain fall out below the hive.
A 2 story 5 frame nuc hive of Russian bees will likely swarm by mid-May even if they are transfered to a larger hive body and oother swarm prevention tools are not used. They build up fast, they will use the stores remaining in those 2-3 frames left over from winter and fill the hive within 5 weeks (5 weeks from mid-February--Willow pollen). They build up so fast and use so much of their stores that even a short temperature inversion can cause them to deplete those stores and starve of starvation.
A Hive that dies of starvation usually has the following tell tale signs: Lots of dead bees head down in the cells, no stores, except maybe some pollen, no brood except in the very last stage and those pupae will have holes in the cells from the bees checking to see if the pupae were still in the white (edible). Bees, during a dearth, will canabalize eggs and pupae in the white, starting with the eggs and working through the brood nest from youngest to oldest unhatched brood until all is consumed and the remaining bees die. So You'll also find the worker bees head down in the brood cells as well as the honey storage cells, dying as they search in vain for an little nourishment.