Newspapers subscribe to wire services. The ability to change headlines and delete content to save space are part of their contract.
However, the comments here by others about newspapers being able to change headlines are entirely correct.
Here's why.
Headlines in printed media have to fit into a certain designated space and that will be different for every newspaper based on a wide variety of factors ranging from font size to placement on the page. One newspaper may run a headline as a single deck across all the columns at the top of the page. Another newspaper may run a two-deck headline across two columns. A third newspaper may make it a four-deck headline across one thin column at the side of the page. Also, in general, headlines at the top of a newspaper page need to be larger than those farther down the page unless there's a deliberate effort to call attention to a package partway down the page.
Those three headlines will all be different lengths, and they may not even share very many of the same words.
All of those factors mean that newspapers will change headlines regularly — and possibly make changes multiple times as the page is being laid out.
That's why copy editors write headlines, not reporters, and the reporter may not even know what headline is going to be used until he/she gets the newspaper the next morning.
The next question is going to be, if there's so much variation from newspaper to newspaper, why headlines tend to be similar if not identical when posted online.
The short answer is that the headline you see on the webpage of a newspaper for an Associated Press or internal newspaper chain wire may not be the same headline you see in the printed edition. In a lot of cases, the AP story gets posted to the web when the newspaper gets it, but the headline could get changed more than once as the page gets laid out, and the story might not even appear in the printed edition at all. Conversely, many newspapers don't put their AP stories online or have them online only for a limited period of time, so just because you see or didn't see a wire service story online doesn't necessarily mean it appeared or didn't appear in the printed newspaper, or that it had anything close to the same headline in print that it had online.