Need Deploying Web Part Solution help

Using Powershell, I'm deploying a .wsp file using the following commands:

add-spSolution -LiteralPath "D:\myDir\Solutions\CompanyName.SharePoint.Communities.AboutUs.wsp"
install-spSolution -identity "CompanyName.SharePoint.Communities.AboutUs.wsp" 
        -webapplication http://devcommunities.swmed.org -GACDeployment

We have multiple web applications:
Communities
Projects
Departments, etc.

The point is to only install/deploy in one Web app (in this case, Communities). However, this installs to every web application. Is this normal?