You dont thnk that Arcane magic is more powerful??
Well technically as defined in the rules the only actual differnces between "arcane" and "divine magic are: Divine magic isnt subject to spell failure, Divine spellcasters gain full access to every spell on their list as determined by their level and (this being purely a roleplaying thing) Divine magic comes from outside sources rather than being learned or internal, as oposed to how Arcane magic is subject to spell failure, and Arcane spellcasters must learn their spells rather than getting them all for free (in other words, Divine spellcasters have at least one automatic advantage over Arcane, and Arcane spellcasters have an automatic disadvantage over Divine)
The specifics of what sorts of spells a class has access to is based on the class, not wether the caster is "arcane" or "divine". Supposedly. Of course in practice when people say "arcane" magic what they mean is "wizard magic" and when they say "divine magic" they mean "cleric magic", and so we will go from that standpoint for purposes of discussion.
Its interesting tho that the Druid has just about as much in common with the Wizard as with the Cleric, magically.
What mass killing spells do clerics have??what one or two, maybe three(I don't have my books in front of me)??
Whats that got to do with anything? "power" and "mass killing" arent automatically the same thing. A casting classes magical power isnt determined solely by how many mass-target attack spells they have.
Take a 10th level mage and tenth level cleric alone in an encounter with 25 base orcs,
A solo encounter with a small mass of vastly inferior oponents isnt an especially good yardstick either.
However to pause and address what seems to be your overall point...yes, wizards/sorcerers/"arcane magic" in the way its generaly thought of are/is better at dealing damage, and especially at dealing damage to multiple enemies. However, as I said above...so what? Thats just one area. Druids who are "divine" spellcasters are in fact almost as good at that.
And Clerics are no slouches at magical offense either, especially from the level range you've mentioned onward. Slay Living, Destruction, Implosion, Harm, Energy Drain, Holy Word etc, Holy Smite etc, and even damage wise Flame Strike, Fire Storm, Searing Light. And then if you count the spells that augment their already decent combat ability and turn them into melee machines...Divine Power, Righteous Might etc etc.
Yes, Wizards have access to more save-or-die type spells, and attack spells in general, but also many of them are more or less redundant. Some may have specific situational advantages over others but some are basically just different versions of the same things. The Cleric has less, but still pretty much covers the bases.
Also as fuin has pointed out, the Cleric can gain limited access to many more wizard type spells via Domains. And if you bring in non core, theres a feat the name of which escapes me, in Complete Divine, that gives them full access to the spells of a domain.
Also, the mage has many spells in with he can become immune to or very resistant to attacks. Stone skin, mage armor, shield, protection from normal missile, and invis come to mind.
And so does the Cleric. In fact as far as protecting from magical attacks, the Cleric is equal or really in my opinion superior. They get all the anti-energy spells plus Spell Resistance, Freedom of Movement (which also makes you immune to being grappled) Death Ward, Spell Immunity, Greater Spell Immunity...
Also they can buff themselves or the other PC's at a lower level than a cleric can.
I'm not sure what you mean about lower level, but yes in terms of buffing combat types other than themselves, a Wizard is actually superior especially as of 3.5 with Haste, Heroism and the like. Really the Bard is probably the king of party melee buffing.
However the Cleric from low mid level on can buff themselves into a combat monster as mentioned above.
The only real advantage that clerics have is they get access to all the spells of the level they can cast, immidiatly(sp?).
Yep, thats one enormous advantage. If you compare the wizard to the Cleric the Wizard is better at dealing damage, especially to multiple oponents, and a little better at overall offense, maybe. Their also better at general utility, especially as far as travel. As far as defense, I'd say their at best tied. The Wizard is probably better at spells that defend against physical attack, but the Cleric is far better at defending from magical and special attacks. The Wizard cannot heal or affect alignment at all. In Divination, again a tie at best, or advantage Cleric considering that they can actually fortell the future, and the have Commune which is safer and more effective than Contact Other Plane. They also have things like Find the Path and Speak with Dead that wizards do not.
And of course on top of this, the Cleric gets full armor prof and the ability to cast in it, twice the HP of the Wizard, good Fort saves, medium BAB, more spell slots and the ability to turn undead (and in terms of non core, thereby gaining access to various powerful "divine" feats)
And this isnt even factoring in the Druid, mainly because they Druid is actually a bit below the other primary casters in magical ability, and gets other things to compensate (as it should be with Cleric but isnt) and also Druids dont really use armor that much, making them less relevent to this discussion.
Point being that overall, "arcane magic" as personfied by the classes in the PH, is not really more powerful than "divine magic" defined the same way. Definitely not enough to warrant the ASF thing.
I agree with those who say its mostly there to maintain the stereotype. I say remove it, or make it apply to every PH class.
I would say do as Monte did in AU and have it be class by class (I especially favor this since to me logically Bards shouldnt have it at all, since 90% of their spells or more should be verbal only) but if this was done the Cleric should have Spell Failure, if used as is. In AU Greenbonds dont suffer spell failure and Magisters do, but Greenbonds are actually noticeably inferior casters to Magisters, whereas in D&D the same is not true between Cleric and Wizard.
But I still think it was initionally(sp?) put in for game balance, and it is a hold-over from that. 
