In D&D 3.x, spontaneous full casters (like the Sorcerer or Oracle) gain their higher level spells a level later than the equivalent prepared caster classes (like Wizard and Cleric). For example, a Sorcerer gets 2nd level spells at Sorcerer level 4, where a Wizard gets 2nd level spells at Wizard level 3.
Why is this? Broadly, I know that the answer is 'game balance', but is there a more specific explanation provided by the game's developers themselves? Are there interviews with D&D or Pathfinder devs where they explain this discrepancy? I've heard the idea tossed around that it was because Monte Cook hates Sorcerers, but I haven't seen any sources to back this up.
This question is not looking for balance analysis of Wizard vs Sorcerer. Multiple such answers have already arrived and been deleted. This question is looking exclusively for developer commentary, the developer's reasons, in their words, not player analysis.
In answering, please make sure that you have sources to back up your claims. The simple answer might be "game balance", but I'm looking for the answer from the horse's mouth, preferably with as much detail about the decision as possible.