DoS isn't exclusive, it was ported to European(?) cellphones a couple years ago. And I think AoS was, too.
AHAHAHAHAHAHAHAA! You can't seriously accept cellphones as a respectable platform for quality Castlevania gaming, do you?

Well I understand your point they aren't exclusive
but cellphones doesn't even register as a worthwhile gaming platform to most Castlevania fans.
Might as well play with paper dolls and colorforms.

But remember exclusivity can change with time. Rondo of Blood was exclusive to PC Engine until it was
ported to PSP and I think WiiStore.
Based on the interviews, from both 1up and a video at E3, it doesn't sound like CV:HD will be a permanent exclusive to 360.
Remember RE4 was exclusive to Gamecube for a time, but it eventually made it's way to PS2.
A game only feels exclusive the first weeks/months it's released. After that, exclusivity can no longer mean anything or hold a game from being ported.
Exclusivity is just used to promote and sell a game more on their console. But that strategy only lasts for so long before sales come to a halt eventually. A console company could care less if a game is ported to another console after they already made a lot of money the first months of its release.
Yes it's true the classic TMNT arcade game was and still is exclusive on X360, but that was a special case.
It doesn't remain exclusive because MS is still paying Ubisoft/Konami/Digital Eclipse, it remains exclusive because Konami and/or Ubisoft or Digital Eclipse decided to not port it to PSN (which is a surprise because I think it sold very well over a long time. Maybe Digital Eclipse wasn't interested in learning to develop games for PS3. But Konami is a different story, they did bring SOTN and Castlevania Chronicles to PSN, even though those were straight emulation, while 360's SOTN had some minor tweaks like new game launch interface and screen options added.)