What Sherlock can't do in the Hound

The lines are from Arthur Conan Doyle's "the Hound of the Baskerville"
For those of you who haven't read the novel *glares*, Dr. Watson was investigating in Baskerville Hall while Holmes "stayed in London". Dr. Watson notices a strange man who lives on the moor and reports him to Holmes--only to find that Holmes was with him all along.
That is my favorite part from the Hound, so I was a little disappointed at BBC's Sherlock because they didn't do it that way. But, after thinking, I noticed that they didn't do it because they couldn't do it.