I don't actually have a problem, but i'm not sure why not?
I used php includes to add a footer and top menu on all my pages, so that I can change them easily. I was expecting that i would then have to change all the .html files to .php, but i didnt. It works fine and its very handy to still be able to check new content locally on the html file before uploading(although without the includes).
Did i just get lucky or does this always work like that?
It sounds like your host had already set up the server to handle it that way, not all hosts do so it is a matter of chance to try it and find it working without needing tweaks. I have seen hosts set up where it cannot work, but not recently.
its very handy to still be able to check new content locally on the html file before uploading(although without the includes)
Go get a pseudo-server like MAMP or WAMP. The basic version is free. It will make your local files behave just like the "live" ones, including oops any includes. And other good stuff like /site-absolute links (leading slash) and directory/ names (trailing slash).