What part of wizards getting memorization would invalidate a sorcerer class that doesn't memorize
No part. Though I don't entirely understand the question - you obviously have something in mind in asking it, but I don't know what that is.
It just means that one of the (potentially) defining aspects of being a Wizard is that act of preparation
I'm denying this. Or, rather, I'm predicting that if D&Dnext has variant spell casting rules for wizards, not all of them will preserve that feature of wizards. Because it is precisely that feature that irritates many people and makes them want variants.
You can't set things on fire with Fireball anyway.
<snip>
I mean, I've been frustrated while playing a pyromancer in 4e by this exact problem.
That's just bad GMing.
Here are the relevant passages from the DMG (pp 65-66):
Like characters, objects have hit points and defense scores (except for Will defense; see Object Immunities and Vulnerabilities, below). . .
An object reduced to 0 hit points is destroyed or otherwise rendered useless. At your judgment, the object might even still be more or less whole, but its functionality is ruined—a door knocked from its hinges or a clockwork mechanism broken internally, for
example. . .
Usually, it doesn’t matter what kind of attack you make against an object: Damage is damage. However, there are a few exceptions.
All objects are immune to poison damage, psychic damage, and necrotic damage.
Objects don’t have a Will defense and are immune to attacks that target Will defense.
Some unusual materials might be particularly resistant to some or all kinds of damage. In addition, you might rule that some kinds of damage are particularly effective against certain objects and grant the object vulnerability to that damage type. For example, a gauz curtain or a pile of dry papers might have vulnerability 5 to fire because any spark is likely to destroy it.
Fireballs set things on fire - especially flimsy gauze and dry paper! What would the [fire] keyword
mean, otherwise?
I am simply making the point that keywords aren't the thing that tethers rules to the reality of the world in 4e.
And I am simply quoting the rules text that contradicts that.
Elemental keywords are largely mechanically insignificant and thus are largely irrelevant static noise.
This is so far from my own experience I'll just have to take your word for it as to how you play your game.
In my game, [fire] damage sets things one fire - as the DMG indicates. The [cold] keyword indicates an effect that cools things down - hence Icy Terrain could be used to freeze a pond or a part of a stream. [Psychic] damage affects the mind and emotions - that's why objects are immune (they have no feelings!). [Necrotic] damage affects living flesh and [poison] damage affects living organs - that's why objects are immune (they're not alive!). If you want to be stealthy, don't use [thunder] damage - it's loud! (That's why bards do a fair bit of it - they should loudly!)
These keywords aren't just for mechanics-to-mechanics interaction. They're the most basic markers, in 4e, of the relationship between mechancial outcomes and fictional outcomes. Ignoring them, and then complaining about the "wrought iron fence made of tigers", seems just bizarre to me. (Also - how would you possibly adjudicate p 42 in relation to magical abilities, unless you had regard to their keywords?)
