Something that I've found curious is that I've recently read news that Samurai Shodown V has recently been released on the Xbox (in the West), and that the remake of King of Fighters '94 is scheduled for launch as well.  However, there seems to be no news (that I can find, at least) of SNK/Playmore bringing the games to N.American/European PS2s?  The reason it struck me as odd is that the PS2 controller seems more intuitive with 2D fighters, so that would lead me to assume that the PS2 console, regardless of location, would be a more desirable market then the Xbox.

This is just a guess, but I wouldn't be surprised if SCEA's unfriendly policy towards games that look dated (read: everything SNK makes) has something to do with it.

I've noticed that more XBox games have online support. Maybe Playmore opted for the XBox market because it has a bigger online user base. Even the 2D fighters Capcom released on the PS2 such as Capcom Vs. SNK 2 and Street Fighter Anniversary Colloection didn't have online functionality while their XBox counterparts did. I don't game online so I can't compare Sony and Microsoft's online services.

Both the PS2 and XBox controllers have 4 face buttons which is really all you need to play Neo Geo games. The PS2 controller does feel a bit more natural though. Just my 2 cents.

This is true. Sony America has a known hostile policy to nearly every pure 2D game out there.  If the game is an older title like many SNK games, then Sony requires the game developer to either sell it as a budget title or to bundle more than one game on it.

There was an game magazine interview with Playmore-SNK American president about how they had to bundle Metal Slug 4 and 5 to be allowed to publish for the PS2 in America.