To expand on this a bit, if you were a prepared caster who could cast 9th level spells in 3e, you were considered a God Tier Class. Quibbling about who was more powerful between Druids, Clerics, and Wizards in 3e was basically about like talking about who is the richest person on earth. What mattered was that you were in the God Tier. So when 4e came and reworked classes: What was the response when the Cleric was brought down to earth? Mostly silence. What was the response when the Druid was brought down to earth? Mostly silence. But what was the response when the Wizard was brought down to earth? Indignant moral outrage that 4e dared to make a God mortal.We know from behind the scene stuff that the lead designer had to fight his own team all the time because they kept trying to make the Wizard more powerful. They debatably overshot in the other direction and the Wizard was probably the weakest class in the PHB, even tho some of the PHB classes used a dual-primary design that was eventually ditched as the game progressed (for exemple, your Cleric could be STR or WIS or both, and Warlock CON or CHA or both). It was the only Controller in the PHB and it didn't really help to define the Controller role very well. The Invoker (Bascally all the Laser from Heaven bits of the Cleric) and Druid in PHB2 were much more well received as far as Controllers went.
4e sent almost ALL utility magic to their Ritual System, leaving mostly combat stuff in the Wizard (they got free Rituals though), and 4e ditched the School of Magic classifications until Essentials shoved them back into the system as a needless keyword addition.
Also, they made Magic Missile an At-Will with an actual attack roll (It was a good one too, inflicted Force damage and had crazy good range).
So... all the Wizard players were pissed their Magicest Magic God King wasn't there anymore.
Fighters, on the other hand, were pretty much one of the best class in 4e from start to finish. They didn't get to be Archer (I mean, you COULD, but it wouldn't do you much good besides ranged marking for a turn) so that was its own kind of bellyaching (if you were too much of a pedant to just play a Ranger for all your Archery needs), but as a Defender they were probably one of the best. Capable of preventing multiple enemies from running past them, having powerful attacks, and even ways to strengthen themselves (Battlerager Fighters could just collect Temp HP at-will if it wanted to! At the cost of Heavy Armor) and the best AC available. For the first time in the game, a Fighter holding the front line ACTUALLY held the frontline! There was no need of a gentleman's agreement with the DM that they wouldn't ignore the Fighter, they just couldn't! And the Wizard (or the Invoker or the Druid) didn't have access to all the broken 3e stuff that would allow them to replace the Fighter, they had to rely on their team mates to hold the line.
So the players used to self-reliant casters were pissed.