The other problem with a single chip being shared by muliple inputs is that it'susually impossible to access more than one port at a time unless you use proprietory software.
I have a 4-port card made by GrandTek, which I'm 99% certain uses the same (Conextent BTCI or something like that) chipset as those cards. Using GrandTek's sofware, I can view all 4 inputs, but using and webcam software, I can only view 1 input at a time, and chaning inputs can only be performed via the WDM or DirectX driver interface.
I recently purchased 6 factory refurb'd DLink DCS900 IP cameras and are very happy with their perfomance. Since they have a built-in server, they run all by themselves. I'm getting rid of the other cameras I currently use with webcam software, with the exception of the "teddy cam" we use as a baby monitor (which is interfaced via a wireless adapter to one port on my 4-port capture card). I **may** expirement with retrofitting one of those DCS900's into the head of a teddy bear and ge rid of the wireless teddy cam all together (the low-light performance of the COLOR DCS900s are better than the B&W teddycam.)