Akira Yamaoka, sound designer and public face of the Silent Hill franchise took part in an interview found in the Wired blog network. When queried as to whether or not the Wii could be home to further installments (more precisely the 5th) he revealed that there was no intention to do so, leaving the reason to the clear fact, that Wii users aren't "hardcore" enough.
WN: What is the future of the Silent Hill series?
AY: We're making Silent Hill 5 for next-gen consoles. Are there any other platforms besides that? [laughter]
WN: There's the Wii.
AY: Ah, the Wii. Wiiiiiiiiii... Silent Hill Wii. Can we do it? Will players like it?
WN: Yeah! There's a lot of potential there, using the remote as a flashlight, or a knife...
AY: Yeah, there's potential.
WN: But no plans.
AY: No plans. The Wii user isn't a hardcore user.
Well there you have it, according to this guy, the Wii is neither a next-gen console or home to hardcore users. Bit of a silly move if you ask me when you consider his inbox if probably full of hate mail by now. But I do love when people say what they think.