If your trying to use common sense then a 'standard'* longsword can not be effectively weilded using two hands. Placing one hand over the other (which is the only way to fit both hands on such a swords hilt) fails to add any leverage for extra damage or weapon retaining purposes.
*for standard I mean short hilted Longswords not Bastard Sword style hilts
Think about it. Do you swing a baseball bat with one hand directly over the other, or side by side with a bit of choke?
I have trained and spared using swords, pikes, spears, staffs, axes, nunchuks, tonfa, etc. Trust me you gain no real benefit to grabbing a small hilt in both hands.
However if you feel that a dagger could be weilded two-handed, then by all means have at it.
IMO, the whole gist of the weapon rules was for sim-pli-fi-ca-tion. Not "But my Longsword has an extra longness to the hilt so I can weild it effectively with two hands" crap.
And yes realistically I find fault with many of their combat rules... Katana requiring a Feat to use effectively one-handed my tail...
TTFN
EvilE