Following the soul ethics thread, I'd like to compare enchanting systems in each game, in spite of game balance probably being the reason why it changes all the time.

In Daggerfall, souls aren't always necessary depending on the object, but they may be bound for more potent enchantments. Use degrades the object and eventually the soul is released. Soul trapping is rather difficult spell. Also, orcs, therioanthropes, vampires, centaurs, giants, nymphs etc are not protected by Arkay's Law and and their soul have various "values".
In Morrowind, souls are always needed, but they recharge enchanted objects over time. Soul trapping is quite easy. A ghost's soul is on par with a scamp, a dremora, an ash slave or acorprus stalker, but lesser than many other daedra, more developed ash monsters and spriggans.
In Oblivion, soul bound objects don't recharge themselves and human souls are equivalent to grand ones.

So maybe some enchanters create a synthetic, functional soul using the material available. This may be what necromancers do, hence bone revenants have petty souls in Morrowind, but souls nonetheless. And it could the same for atronachs using alchemy.

I find the difference between Morrowind's near human souls and Oblivion's definately human souls quite odd. I thought it was just done because we're humans and we're awesome, so we should have the best souls short of the Tribunal. Corprus monsters' souls appear to grow over time rather than degenerating so I assumed that human souls were common, especially if ghosts are simply souls in ectoplasm. Are post Morrowind souls "souls" or "souls"?

Souls are a type of magic; note the relation between Aetherius, the Dreemsleeve, and Magnus. Also note that Merida is a 'daughter' of Magnus. The idea of souls is thus a subgradient of the idea of magic. This said, the magic from the soul can be converted into the more 'magicy' type of magic and vice versa. Soul trap does just this, and Necromancy does the opposite.

All things in Nirn are powered by magic. The very sun itself, the source of all life on the planet, is just one massive rift into Aetherius were all magic pours from. Life in this world is plainly magic-based; with the souls of all living things nothing more than weakened deities whose godhood has diminished over generations of breeding, mutation, curses, and apotheosis. Persons, the races of Men, Mer, and Beast have the strongest souls closest to divinity, granting them special privilege in the hierarchy of things including sentience. As we've been shown, it is possible in many ways for people to become gods or god-like themselves, returning to their lost-divinity. Or, degenerating to a lesser state.

So to answer your question, it depends on how you're willing to bet your humanity.