Hi Leslie, most photography articles on composition speak in generalities that may or may not apply evenly to all scenes. One of the biggest advantages of having something interesting in the foreground is to provide a sense of depth. If the scene is relatively flat in appearance, that can be an effective tool to use. Comparing your two images, you can see that the appearance of the second one is flatter than the first. The question isn't as much about depth as it is about how you want to composition to look.
For example, take a look at Donald's
From Sea Thrift to Jura. His use of a wide angle lens to bring objects that are inches away from the vantage point with objects that are miles away provides a phenomenal sense of 'being there' through the use of detailed foreground objects.
On the other hand, this
Sunrise image has nothing in the foreground.
It comes down to learning the tools and techniques that are available to you and applying them appropriately to the scene at hand. The 'rules' of composition are there for a reason. They work quite well in most circumstances so they provide an excellent starting point to learn how to take interesting pictures. As your skills improve, you learn how to employ those learned techniques to get the most out of a scene, and that includes breaking the rules when it is appropriate to do so.
Here is a good 'rule' to consider for learning landscape photography. I call it Frank's Rule of Thirds for Landscapes. Have something interesting in the foreground, middle ground, and background. Should you ever break the rule? Of course!