The Sphere spell is quite different from the Wall in many ways. One of them being that the Sphere isn't air tight. Or is it? Does it act as a filter, so poison gasses are kept out but breathing isn't impaired? Does it offer some sort of life support instead?
I hate applying Physics to D&D, but...
1st second of falling, 32 feet per second, 32 feet fallen.
2nd second of falling, 64 feet per second, 96 feet fallen.
3rd second of falling, 96 feet per second, 192 feet fallen.
4th second of falling, 128 feet per second. 310 feet fallen.
5th second of falling, 160 feet per second, 470 feet fallen.
6th second of falling, 192 feet per second, 662 feet fallen. (With the caveat that these speeds ignore wind resistance and terminal velocity.)
Oh I agree, though the duration, which is measured in minutes, is borderline too short to really do that.
And it's funny because, as written, it would allow someone to breath "normally" in places where they normally couldn't. We don't see much D&D in the vacuum of space, but under water? In toxic gas clouds? The summary description in the spell index says it "protects but traps" a creature.
Ironically I'd considered it as part of a death trap, popping one on a foe who was already inside a Cloud Kill, trapping them inside with it for what would probably be the rest of their life.. But, as written, the Sphere would save them from it instead.
And it's perfectly natural to die if stabbed 27 times with a dagger, yet they don't refer to such a death a s"Natural". It would be pretty unnatural not to die from such serious wounds in fact.
So support your local medical examiner: Die strangely!
PHB said:Otiluke’s Resilient Sphere
Evocation [Force]
Level: Sor/Wiz 4
Components: V, S, M
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Effect: 1-ft.-diameter/level sphere,
centered around a creature
Duration: 1 min./level (D)
Saving Throw: Reflex negates
Spell Resistance: Yes
A globe of shimmering force encloses a creature, provided the creature is small enough to fit within the diameter of the sphere. The sphere contains its subject for the spell’s duration. The sphere is not subject to damage of any sort except from a rod of cancellation, a rod of negation, a disintegrate spell, or a targeted dispel magic spell. These effects destroy the sphere without harm to the subject. Nothing can pass through the sphere, inside or out, though the subject can breathe normally.
The subject may struggle, but the sphere cannot be physically moved either by people outside it or by the struggles of those within.
Material Component: A hemispherical piece of clear crystal and a matching hemispherical piece of gum arabic.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.