If you look at what bumble bees do, you may find an alternate explanation for why the colony starts out raising small bees and gradually increases their size. The bumble bee queen raises very small worker bees early in the season but as the colony begins to prosper, they are born larger and larger, presumably due to increased feeding. 

This may reflect the need to produce many bees quickly early in the season. Later, when resources are available they may attempt to produce "better" bees. Ultimately, the bumble bee colony raises full sized queens and males. This could be paralleled in the honey bee colony. Early on, they may attempt to conserve resources by using less wax, hence making smaller cells, and using less food in making smaller bees. 

Then, when the hive begins to prosper they greatly enlarge the cell size and begin to build comb after comb of drone cells. These are available to be used for raising drones or for honey storage, depending on how fast the honey comes in. I have given foundationless frames to my hives all season and I notice that when the honey flow is really good, the drone comb gets filled in with honey, perhaps before the queen can find the open cells.

PLB

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