Yes, really: the BBC had a policy of destroying their old tape masters up through the late 70s, at least. A lot of series fared much worse than Doctor Who, which was being widely sold to other countries—there's at least one show from that era of which no episodes remain at all.
Similar stuff has happened in other countries: most of the output of one of the pioneering US television networks was lost when Paramount, who bought them out, disposed of the remaining tapes (again in the 70s)—out of what must have been 10000+ hours of programming, we have maybe two or three hundred. Other shows, like game shows or news programs, were often considered disposable in the pre-VHS era, and junked even by networks that normally kept their tapes. Cinema hasn't fared any better, especially black-and-white silent films—the silver nitrate film stock they used in those days is highly flammable and was often destroyed to reclaim the silver content (and that's aside from normal deterioration). It's really sad—not so much due to the quality of the shows (although some of them must have been excellent), but because of the loss of history.
