The Eschew Materials feat has quite a long history. From my research, it's been printed in at least eight different sources from v3.0 to v3.5 to PFRPG. In all of the v3.0 printings, it was listed as a Metamagic feat. Then in the v3.5 PHB it was changed to a General feat. PFRPG kept this v3.5 classification as a General feat.
2001 - Tome and Blood - Metamagic
2001 - Lords of Darkness - Metamagic
2001 - Magic of Faerun - Metamagic
2002 - Dieties and Demigods - Metamagic
2002 - Faiths and Pantheons - Metamagic
2002 - Epic Level Handbook - Metamagic
2003 - Player's Handbook - General
2009 - Pathfinder Core Rulebook - General
Rules-wise, it seems pretty clear that it is no longer a metamagic feat. Does anyone have any good theories as to why the change? Is it just because the level adjustment is zero instead of a positive number?
What seems strange to me is that the similar feats for easing casting components (Still Spell and Silent Spell) are still Metamagic but the corresponding feat which removed the material component requirement (Eschew Materials) is a General feat.
Of course, it's very easy to have a house rule changing it back to a Metamagic feat. I'd just like to hear theories as to why the change was made by Wotc in v3.5. It was pretty clearly a conscious decision after six separate printings as a Metamagic.
Because it doesn't matter as a metamagic feat. It has no level adjustment and doesn't help with spells with important material components. It's a hand wave feat -- something that gets rid of the need for a general spell component pouch.
Now Still Spell allows more than what eschew materials does -- it allows casting while you can't move, or while in heavy armor, or in forms that can't do somatic components. It has more use than eschew materials since it allows spell functions at times they normally can. Silent spell is the same way. They have level adjustment because they actually adjust how you can use a spell.
Now Energy substitution is also a 0 level adjustment but it has an actual in game effect: Namely spells that couldn't affect targets now could or could do more damage. That's significantly different than replacing a 15 gp mundane almost always accessible item with a feat.
Also as a "non metamagic feat" it does have companions -- Augment summoning, spell penetration, and spell focus for examples.
It has a broad effect on all spells under a certain purview instead of a limited one on select spells: It's almost always active, where as metamagic feats are not.
Cinematically, speaking arcane gibberish while flourishing grand arcane gesures is a staple of just about every movie wizard I've ever seen, from Gandalf to Harry Potter and dang near every wizard in between. Trivializing verbal or somatic gestures is, er, uh, unnatural.
But I don't remember very many (if any) movie wizards (or even novel wizards) hurling sand and lint and bat guano all over the battlefield. Trivializing the annoyance (and dependence) on stuff you have to procure and carry everywhere you go seems like a great idea to me, and not the least bit unnatural.
Now, remember that sorcerers and wizards have different rules about metamagic, and making Eschew Materials a zero-level Metamagic feat would be unfair to sorcerers. Either trivialize it or don't, but don't trivialize it unfairly across the classes.
In 3.0, a wizard could choose it as one of his bonus feats. In 3.5 and Pathfinder, he cannot.
This would likely be the difference the OP is concerned about.
A Metamagic feat is something very specific: it's a feat that lets you change individual spells by adding an additional quality to them. Every Metamagic feat is applied selectively to spells according to the caster's wish.
Other feats may affect the way in which you cast spells, such as Spell Focus, Spell Penetration, Spell Mastery, Combat Casting, Arcane Armor Training, and yes, Eschew Materials. These feats are not applied on a case-by-case basis to spells; they change something about you, the character, that involves spellcasting. If you selectively apply a feat to spells, it's metamagic. If it changes how you cast the spells generally, it's not.
And, as already pointed out, the Sorcerer would have to use a full-round action to cast a "Componentless Spell" as metamagic, which seems unnecessary.
By the way, I usually do allow my wizards to take Eschew Materials as a wizard bonus feat if they so choose.
Yes, one of my favorite progressions used it as a prerequisite metamagic feat.
They should include a special clause at the end of the feat that allows it to count as a metamagic feat for the purpose of bonus feat selection and meeting prerequsites.