You should use PowerShell for provisioning your service apps. For once, you do not always know where your SA's will end up depending on farm topology (dedicated application server etc), so automated farm configuration should be done in PowerShell.
An example (taken from Todd Carter's blog, but there are several examples out there)
Write-Host "Creating Web Analytics Service and Proxy..."
$stagerSubscription = "<StagingDatabases><StagingDatabase ServerName='$databaseServerName' DatabaseName='StagerDB'/></StagingDatabases>"
$reportingSubscription = "<ReportingDatabases><ReportingDatabase ServerName='$databaseServerName' DatabaseName='WarehouseDB'/></ReportingDatabases>"
New-SPWebAnalyticsServiceApplication -Name $WebAnalyticsSAName -ApplicationPool $saAppPoolName -ReportingDataRetention 20 -SamplingRate 100 -ListOfReportingDatabases $reportingSubscription -ListOfStagingDatabases $stagerSubscription > $null
New-SPWebAnalyticsServiceApplicationProxy -Name "$WebAnalyticsSAName Proxy" -ServiceApplication $WebAnalyticsSAName > $null
Get-SPServiceInstance | where-object {$_.TypeName -eq "Web Analytics Web Service"} | Start-SPServiceInstance > $null
Get-SPServiceInstance | where-object {$_.TypeName -eq "Web Analytics Data Processing Service"} | Start-SPServiceInstance > $null