Exactly, and why it's probably the only SciFi series that has gone from circa 1962 through to 2013. You just get bored I reckon when something is intellectually trash (unless you're intellectual trash ;-)) I think they've proved that viewers want something that keeps them interested and doesn't consider them fools.
@Etmax: BTW are you sure the relaunch is Fox and not BBC??
The main relaunch in 2005 was by the BBC. I think the earlier comment about the Fox Relaunch referred to the one-off film in 1996 that was hoped to kick things off agaon. That was developed as a co-production between the BBC, Universal Studios, 20th Century Fox, and the American Fox network.
@Etmax: I think where a lot of writers go wrong is they start of really good with a game plan in the first season not really expecting it to go far...
That's what I like about Dr Who -- especially the past few seasons -- when you go back and rewatch them you see that there are clues in the early episodes that tie in to things at the end of the season (sometimes in future seasons)