Not really. The extra +1 proficiency bonus a longsword has over a staff compensates for using a magic sword that is five levels lower than the character. With the pricing of magic items in 4E, you can get an item 5 levels lower for next to nothing...especially if it is the fighter's hand-me-down sword that he no longer uses because he got a new one. By using a staff in two hands, you can't use a second implement or a shield, and you do less damage than the longsword.
Less damage?
A +3 Staff with a 10 Str Wizard does D8+3 damage and is lvl/2+5 to hit. A +2 Longsword with a 10 Str Wizard does D8+2 damage and is also lvl/2+5 to hit.
So, the +3 Staff does more damage unless the +2 Longsword is used two handed. In that case, the Wizard typically cannot use a second implement either.
The +3 Orb (9000 GP) and +2 Longsword (1800 GP) is worth more than the +3 Staff (9000 GP). Granted, the +2 Longsword can only be sold for 360 GP, but that's still 360 GP.
Just a small difference, but "not zero".
By using a staff in two hands, you can't use a second implement or a shield, and you do less damage than the longsword.
While mostly true (the longsword does not do more damage unless it is the same plus, in which case it would be 9000 GP implement plus 9000 GP longsword in the above example), it's somewhat irrelevant in some cases. Some Wizards do not use a shield or a second implement, nor have the feat to use a longsword.
One reason to take a Staff Wizard is because the player is not planning on using a shield or using a longsword. And if a Staff can be used as an implement one handed, then a Wizard could use a shield with it (he just couldn't OA or attack with it, but, who cares?).
Even a player planning on taking a second implement is not really at a significant disadvantage. It only takes a minor action to pull a second implement out and another to put it back away again. Since Wizards tend not to fight in melee, it is relatively rare for one to use a Staff that way anyway. Usually, any melee attack from a Staff Wizard is an OA.
Granted, most wizards won't bother using a weapon, because their at-will powers are better. However, Eladrin get longsword proficiency for free. It'd be nice to see them be able to use their proficiency without restricting their implement choice or forcing them into Wizard of the Spiral Tower.
True.