PS3 cannot presently stream video from the sources you want.
I went with the new Mini running Plex even though I had a PS3 already - it's just not suited for streaming media yet because Sony doesn't support it.
There are little "apps" you can download direct from Plex that allow you to stream content, including Hulu, Netflix, NBC, Quicktime trailers, Comedy Central, BBC, and many, many others. Works perfectly.