There is an excellent PDC talk available here from Vishal Joshi which describes the new MSDEPLOY features in Visual Studio 2010 - as well as how to deploy an application wit
I had a similar problem and the solution was to have the following parameter:
/p:MSDeployPublishMethod=RemoteAgent
Here are all of the parameters I used.
/p:DeployOnBuild=True /p:DeployTarget=MSDeployPublish /p:MSDeployPublishMethod=RemoteAgent /p:MsDeployServiceUrl=http://my-server-name /p:username=myusername /p:password=mypassword
NOTE: I'm not using DeployIisAppPath because I'm building a solution and trying to build three web applications at once. Also I think your MsDeployServiceUrl should be just http://staging.example.com
It appears that when using InProc (which may be the default) for the MSDeployPublishMethod MSBuild ignores MsDeployServiceUrl and always tries to deploy to the local server. I changed it to RemoteAgent and all three of my web applications deployed successfully. I did notice that the Package file is nolonger contained in the MyWebApplication_Package folder, but that isn't a big deal to me.