I guess namsupo already covered most of this and his reply got in before mine, but here's mine anyway in case the little ASCII diagrams are helpful. :-)
Hardlinks would be ideal for me if their behavior was consistent.
Unfortunately, because they don't always work, I've had to find other ways of achieving similar results.
Their behaviour is consistent. If it wasn't it would be very worrying for a filesystem feature! :-)
What isn't consistent is how you (indirectly, via the programs you use on your files) are interacting with the hardlinked files. A hardlink to a file is simply an additional filename which points to the same data that the original filename pointed to.
When you create a file normally you are, without knowing it, effectively creating a hardlink which associates a filename with some data (the file contents):
FilenameA -> [Data1]
If you then create a hardlink you will have two names both pointing to the same data:
FilenameA -> [Data1] <- FilenameB
Hardlinks point to data and not to filenames! FilenameB is pointing to the same data as FilenameA but it is not actually pointing to FilenameA. (That would be a symbolic link.) If the meaning of FilenameA changes it has no effect whatsoever on FilenameB.
If you delete FilenameA but leave FilenameB then you're left with this:
FilenameB -> [Data1]
If you now create a new file and happen to call it FilenameA then it's a completely separate file. There is no connection at all between FilenameA and FilenameB:
FilenameA -> [Data2]
FilenameB -> [Data1]
So when Word deletes the old file and then saves a new file with the same name that's what happens. If Word instead overwrote the old data with the new data, without deleting or creating any files, then the problem would not occur.
Of course, you often cannot change how a program saves its files. (Sometimes you can, sometimes it's out of your hands.) So using links like this isn't a good idea and can lead to confusion. Links in general can lead to confusion and shouldn't be used gratuitously. (Symbolic links and shortcut files are less of an issue). But while I recommend that people don't use the things when it isn't necessary, the way hardlinks work is completely consistent and well-defined.