Ajbuckly, I'll try to address some of your questions as best I can. I'm by no means an expert, but I do find it interesting to discuss ratings, and analyze what people watch.
CW is a '5th' network in the US and it caters to a much younger demo. It has had several very successful shows, such as 'One Tree Hill' and 'Gossip Girl', which are teen soap operas; 'Supernatural' and 'Smallville', more syfy in nature, and a new 'Vampire Diaries', which is doing very well. All these shows are very popular among the 18-35 crowd, and even younger. They only get 3-5 million viewers per episode, but I suspect 90% of their viewers are in their target demographic. They are actually pretty good shows, and with young actors that are cheaper to employ.
Regarding the L&O and ER demos, I would say that anything under a 2.0 in the 18-49 demo is terrible, 3.0 being decent. But CSI needs to be closer to a 4 to be successful on Thursday night, which is the most competitive night for advertisers.
And addressing the older demo who is home watching tv over the weekend? The advertisers would rather they were out spending money. lol. In the US on Saturday nights, it's primarily reruns.
I'm not a 'Sex and the City' person, but I do like sci-fi, when it's done well; mostly, I like good storytelling. But I'm in the older demographic, so the networks probably don't care what I like. :lol:
What I do see happening is that networks are identifying themselves with certain viewers, and will cater to those viewers. Cable networks do it already, and the mainstream networks to a lesser degree: ABC has a more youthful image, CBS is the older, crime/procedural image, and NBC is the young and quirky one. NBC is struggling now because of this image, and maybe it's not mainstream enough, but I do like a lot of their shows, including 'The Office'.
I think the crime drama will be a popular genre for years to come. CSI will need to stay current with their technology and interesting with their storytelling, but the characters are what will attract viewers. People aren't awed by the technology or the gruesome crimes anymore (many shows have these); instead, they will be drawn in by interesting characters. I know CSI doesn't like to get personal, but I think it needs to in order to stay successful. On the other hand, they could consider themselves the blueprint for crime shows (like Gunsmoke was for westerns), not change a thing, and be satisfied that they have had a great run and a huge impact on television. I just hope that when CSI goes out, it goes out at the top of its game.