ER, The Simpsons, etc.

The Simpsons is about to go off the air pretty soon and ER rating are getting lower each year, the only exception is law&order which became a cult series (and can attract young good actors and cheap actors for minor parts which make it better) . So the end is some what near for these two (ER & Simpsons), although television series can go on for a long time (day of our lives etc.) it usually applies for soap operas with low production (and high addiction) value. But big productions will find it hard to survive such a long time, even law & order made spin-offs to attract more hype.