Speaking as both a frequent GM and a slightly-less-frequent player of spellcasters, I feel like JoT's overstating the problem.
In my experience, there are multiple valid approaches to most problems, and I can use my spells alone or in combination to solve those problems. If I focus on the low-end spells, then my fighter buddies will be carrying a little more of the weight for that encounter. If I focus on the high-end spells, then my fighter buddies will be carrying a little more of the weight in later encounters. JoT makes it sound like a wizard's player is making a critical, stressful choice every time he casts a spell; if that's the case, he needs to invest in some wands or staves. These magic items give you something to do when you don't know what to do, and let you conserve your spells for when you're actually in a jam. But then, the thing I love most about being a wizard is always having just one or two more tricks up your sleeve.
As a GM, I can scale encounters within a day more sharply. That is, if the PCs have held onto their high-end spells all day in preparation for that last encounter (and you know they've been in the habit of doing so), then let that last encounter be one where they're happy they did so. But if they've already burned those spells for whatever reason... well, the wizard and the cleric (or other Vancian casters) aren't the only party members who can destroy enemies en masse.
I'm looking forward to 4e, but I feel like JoT's getting a little carried away with recognizing the problems of 3e. Giving players meaningful choices to make in each round of combat isn't bad game design, though I think it may be falling out of vogue.
Haven