Can't be said any better. Mike you are good (successful) at explaining your point.

When I said not accurate I did not elaborate, which you did nicely. In software delays accuracy does not come as simple as the repeatability. To acheive good results it needs lot of effort to code properly, due to the reasons you stated. Software delays are useful in many instances, which can be achived in few lines of code when timing need not be accurate. However, when accurate timing is required interrupt based method suits better. Because (mostly) it is not affected by the conditions said in your post. There may be exceptions which I don't know. Please correct me if I am wrong.