When people (including me) complain about "Vancian casting", they're actually complaining about two things:
1) That ALL of a spellcaster's resources are daily-use, and furthermore that a spellcaster is not restricted to how often he can otherwise tap those resources. The root cause of the "five-minute workday" (which is really a different but related issue) is that the game's assumption is the Wizard will expend about 1/5th of his spells in a single encounter (and use a crossbow or otherwise do nothing the rest of the time) and thus will be "functional" for four or five encounters before he needs to rest. However, the reality is that the spellcaster blows through all of his resources in only one or two encounters, either because doing so makes those encounters significantly easier and conserves other, less-renewable resources (hit points), or because doing so is necessary just to survive the encounter.
4e's solution to this was rather elegant, actually: give the spellcaster 1/5th as many resources, but let him use them in every encounter. A useful compromise might be to restrict how many spells a character can cast in a single encounter, but that would run into the same kind of verisimilitude issue that people take with 4e's system.
2) That not all classes work on this system. Why are Fighters linear and Wizards quadratic, as the saying goes? Because Wizards (generally, spellcasters) have the ability to expend a huge amount of their resources in a very short amount of time in order to gain a disproportionately massive "peak output". Fighters (nonspellcasters) do not possess this ability to "go nova"; they are restricted to a baseline efficiency over time ratio that they cannot voluntarily alter. The spellcaster can proportionally increase (or reduce) his output based on the requirements of the encounter, the nonspellcaster cannot. Additionally, this creates a situation in later levels where the spellcaster's baseline efficiency outpaces the nonspellcaster's: even if the spellcaster plays for par (1/5 of his resources), his output exceeds the nonspellcaster's because his efficiency rises more quickly as he gains levels than the nonspellcaster's does.
Whatever the nature of the decisions made during the design process of DDN, this is an issue that will have to be addresses. If Wizards is smart, they'll address this quickly, and loudly.