Lets face it - there are people who care more about post count than using the edit button. There are people who use multiple posts instead of consolidating replies into a single post purely for post count. I, an probably a few of the other mods as well, have at times merged them. One particular example I merged about 8 consecutive posts into one. However, most of the time I can't be bothered - I have better things to do.
The real benefit of this is in preventing those people who join a thread that has reached page 5, and start at the very start of the thread putting in quote comments about many of the points made. They end up with about 4 or 5 posts in a row, and some of these are one-liners. Why shouldn't they all be merged in to one?