We can indeed add a counter, and it would not be difficult to do. However there are two problems.
First, we can not add a unique view counter - one that counts each individual once. Therefore, if someone refers back to a given post repeatedly, each trip back counts as a new count.
Second, since people can change the way they view the forum from threaded to "flat" (meaning that they see all the messages in a given thread on a single page), anyone using that option would drive up the counts even if they did not actually read all the posts.
In both cases, the counter would over-estimate readership.
Lastly, and this is just my opinion, if you have something to say, you should just say it and not worry about whether anyone else actually reads it. That's just not the point of the forum.
But that's my opinion.
Don