Well, the important part of what sIKE is suggesting (in my opinion) is to block Line of Sight cheaply. For this task, a Fog Bank would work fine. Wall of Earth is superior to Fog Bank if you ask me, however, because it also blocks passage. This makes it more difficult to circumvent. Both have the options of going around or destroying the wall, but Fog Bank can also be gone through which the Wall of Earth can't.
In addition, the Wall of Earth is in school for more mages (Warlord and Earth Wizard) than the Fog Bank (Air Wizard). Plus the previewed card
Otto Kronig can put armor on the Wall of Earth and reconstruct it. The Goblin Builder is also meant to be able to reconstruct it, although there is concern that it can't as currently worded. Fog Bank lacks this kind of support.