Actually, I'd like to read the article about the play without finding out the ending. Is that an unreasonable thing to ask?
Reading the article as it appeared on 26 July 2010, [1] there is an entire section called "Identity of the murderer"... If I did not want to learn the identity of the murderer, I would have skipped over this section.* That's what I did for years before I became an editor. If I suspected a section would contain spoilers, I skipped it. When looking up books I plan to read, I still do this.
That's one of the reasons for sections - they can allow readers to quickly find just the info they are looking for. I can look up Harry Potter and the Deathly Hallows [2], and if I didn't want a spoiler but wanted to read about pricing problems, there is a section in the Table of Contents, right at the top, called "Price wars and other controversies". This allows me to bypass the "Synopsis" section, including the subsections "Plot introduction" and "Plot summary".
Perhaps this is not the way everyone reads, but I think context clues can give their own warning to the reader.
I'm also not sure if there are any articles out there that have spoilers under a section you might not expect them to be. For example, I wouldn't expect to find a spoiler under the "Release date" section. But I also can't think of a good reason why it would be there anyways, and it should probably be moved to the plot section(s).
Just my two cents. :) -User:Avicennasis
[1] http://en.wikipedia.org/w/index.php?title=The_Mousetrap&oldid=375574290#... [2] http://en.wikipedia.org/wiki/Harry_Potter_and_the_Deathly_Hallows
*A quick glance did not show this information to be listed in any other section, however I did not read the whole article word for word to double-check.