[quote=@GreivousKhan]
<Snipped quote by MelonHead>

I wouldn't say you [i]need [/i]a horse. In fact, a Samurai largely being a horse archer, has less business being on foot with only a sword than a knight (who historically dismounted for sieges anyway.) yet they pull it off pretty well. (perhaps unreasonably well from a historic stand point, they don't even get the option of a shield after all for some absurd reason)  
[/quote]

Yeah, I've recently been on a semi-crusade to discover why the Japanese never bothered with shields, I've still not heard any fully convincing arguments. (other than the fact that almost all their mainstream weaponry was traditionally used two handed.)

I think the difference is the 'primary' weapon of the Knight was the lance (as far as I'm aware, anyway) which is pretty much completely unusuable on foot. The Yari, Naginata, Konabo, Katana, No Daichi etc etc were all of significant use on foot, most were actually designed for it. The Samurai only had to be on a horse for mobility, no other reason really. 

To be fair, I doubt Knights besieged castles all that frequently historically, that was the job of the peasants. Except during the Crusades I suppose, though one Crusade did end with the *Holy Roman Emperor, Fred falling in a river and drowning because of his armour, which is really irrelevant but a favourite fact of a friend of mine.