Dr. Who was off the air for nearly two decades, though; that's hardly the same thing as The Simpsons or Law and Order (Family Guy and Futurama are arguable, I suppose; they both stopped too, though in mid-decade rather than before it started).
Yes, Doctor Who was off the air for nearly 16 years, but still, it has been on air for 30, which is longer than any of the other shows in the poll.
The problem is that, legally, the current
Doctor Who is a separate television program than the original; they merely share a name. Now, certainly, they feature the same main character and are set in the same continuity, but they are still legally separate productions. And the current series began in 2005, whilst the original series ended in 1989.
Meanwhile, you're
all forgetting about this little show called
Saturday Night Live that's been going strong since the mid-70s.